Radiation-activated cytotoxin therapy of neoplastic disease

ABSTRACT

A method of treating neoplastic disease wherein a patient in need of such treatment is administered an effective amount of a radiation-activated cytotoxin prodrug (RACP) which has low toxicity, which is reducible by reducing agents generated by the radiolysis of water and which, upon reduction, releases a sufficient amount of a cytotoxic effector of sufficient cytotoxic potency to kill tumor cells. The tumor cells are irradiated with ionizing radiation to reduce the prodrug which is present at the locus of the tumor cells to release the cytotoxic effector.

This application is a 371 of PCT/NZ96/00085 filed Aug. 19, 1996.

This invention relates to cancer therapy. More particularly, it relates to the use of ionising radiation to activate drugs to form cytotoxic species in hypoxic microenvironments, to methods of treating neoplastic disease, to a new class of compounds for use in such treatments and to methods for preparing these compounds.

BACKGROUND TO THE INVENTION

Ionising radiation is widely used to treat neoplastic disease, but its effectiveness appears often to be limited by the presence of radioresistant hypoxic cells in tumours. At present there is no generally-useful method for eliminating these hypoxic tumour cells. One approach, being evaluated clinically at present, is the use of compounds which are selectively toxic to cells under hypoxic conditions. The most important compounds of this type are known as bioreductive drugs (BD) because they are activated metabolically by enzymatic reduction to form cytotoxic products under hypoxic conditions. In general, the selectivity of these compound, to hypoxic cells is a consequence of reoxidation of the initial one-electron reduction product by dioxygen, resulting in futile redox cycling and suppression of net reduction in oxygenated tissue.

The mechanism of activation of most BD is as follows: ##STR1##

BD are however likely to have two main limitations in clinical use.

The first of these is that enzymatic activation of BD is not restricted exclusively to hypoxic environments in tumours, and these drugs will therefore have some toxic effect against normal, well-oxygenated tissues. In particular, reductive activation by oxygen-insensitive pathways (obligate 2-electron reduction, which bypasses the O₂ -sensitive intermediate) may sometimes be a limitation.

A second limitation of BD is that, to be effective, enzymes capable of activating the bioreductive drug must be expressed at a high level in the tumour. This is not a condition which will be met by all tumours.

An alternative approach involving activation of a prodrug was reported by Nishimoto et al in J. Med. Chem 35:2712-2715 (1992). In this approach, radiolytic activation of a 5-fluorouracil (5-FU) dimer was suggested as a radiosensitisation strategy in mice. However, it is apparent that radiolytic activation of the reported 5-FU dimer would not be clinically effective as the yield of cytotoxin was too low (a theoretical maximum yield in the order of 2 μmol/kg at the radiation dose used (20Gy)).

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a method of effectively treating neoplastic disease which is not subject to the limitations of BD therapy, or at least to provide the public with a useful choice.

Accordingly in a first aspect, the invention provides a method of treating neoplastic disease which comprises the steps of:

(a) administering to a patient in need of such treatment an effective amount of a radiation-activated cytotoxin prodrug (RACP) which has low toxicity, which can be reduced by reducing agents generated by the radiolysis of water (the aquated electron and/or the hydrogen radical) and which, upon reduction, releases a sufficient amount of an effector of sufficient cytotoxic potency to kill tumour cells; and

(b) irradiating said tumour cells to reduce the prodrug which is present at the locus of said tumour cells to release said cytotoxic effector.

The RACP can be of formula I ##STR2## wherein R¹ represents H or C₁ -C₄ alkyl optionally substituted with hydroxyl, ether, amino, methylamino or dimethylamino groups;

n is 0, 1 or 2, and each M is independently selected from NO₂, CF₃, CH₂ OR¹, COR¹, CONHR¹, OR¹, NR¹ R¹ and SO₂ R¹ wherein R¹ is as defined above;

wherein arom is a single benzene ring or a 5- or 6-membered aromatic heterocycle containing one or two heteroatoms independently selected from O, S and N;

L⁻ can be any pharmacologically acceptable counterion;

K is H or Me;

and wherein R² is represented by:

(i) a radical of formula II ##STR3## where X is halogen or OSO₂ R¹ (where R¹ is as defined above);

A and b are each H or collectively represent an optionally substituted fused benzene or pyrrole ring system;

W is selected from SO₂ R¹ (where R¹ is as defined above) and the structures IIa and IIb, where:

D is CH or N;

E is NH or O;

each Q is independently selected from OR¹ and NR¹ R¹ wherein R¹ is as defined above;

n is 0, 1, 2 or 3; and

HET represents a 5- or 6-membered carbocycle or heterocycle containing one or two heteroatoms independently selected from O, S and N;

(ii) a radical of formula III ##STR4## where X, A, B, Q and n are as defined above; and each D is independently CH or N; and

each E is independently NH or O;

(iii) a radical of formula IV ##STR5## where Z is H or NHR¹ (where R¹ is as defined above); n is 0, 1, 2 or 3; and

each Y is independently selected from Me and OMe; or

(iv) a radical of formula V ##STR6## where each J is independently H or OH; and T is NMe₂ or a moiety of the formula ##STR7## wherein n, M, arom, K and R¹ are as defined for formula I above.

A favoured subset of the compounds represented by formula I is represented by formula Ia ##STR8## wherein R² and L⁻ are defined as in formula I, and M is one of H, CF₃, CH₂ OR¹, COR¹, CONHR¹, OR¹, NR¹ R¹ or SO₂ R¹ where R¹ represents H or C₁ -C₄ alkyl optionally substituted with hydroxyl, ether, amino, methylamino or dimethyl-amino groups.

Alternatively, said RACP can be of formula VI ##STR9## wherein each R¹ is independently as defined above; U and V are both CH₂ CH₂ Cl, or U is H and V is a compound of formula II or formula III as defined above;

L⁻ is any pharmaceutically acceptable anion.

In a further alternative, the RACP can be of formula VII ##STR10## wherein M, n, arom and L- are defined as for formula I.

In a further alternative, the RACP can be of formula VIII ##STR11## wherein Y and Z are as defined for formula IV, T is Co(III) or Cr(III), n is from 2 to 6, m is 2 or 3, and R³, R⁴, R⁵ and R⁶ are each independently selected from CN, halogen, SCN, H₂ O and NHR¹ wherein R¹ is as defined above, or together represent 3-R⁷ acetonylacetonato (where R⁷ is H, Me, NO₂, CN, SCN or SPh [where Ph is a benzene ring optionally substituted with up to two groups independently selected from Me, OMe, NO₂ and NMe₂ ]).

In all of the above definitions, where enantiomeric or diastereomeric forms are possible, all such possible forms are included.

In still a further aspect, the invention provides RACP compounds of general formula I as defined above.

In another aspect, the invention provides RACP compounds of general formula VIII as defined above.

In yet another aspect, the invention provides a pharmaceutical composition suitable for use in a method of treating neoplastic disease as defined above which includes a RACP compound of formula I, VI, VII or VIII and a pharmaceutically acceptable carrier or vehicle therefor.

In a final aspect, the present invention provides methods for preparing compounds of the general formulae I or VIII as defined above. Such methods are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

While the invention is broadly as defined above, it will be appreciated by those persons skilled in the art that it also includes the specific embodiments described below. These specific embodiments are described in conjunction with the accompanying drawings in which:

FIG. 1 shows the effect of radiolytic reduction of compound 1 (bis(3-methyl-2,4-pentanedionato)(N,N-bis(2-chloroethyl)ethylenediamine)cobalt (III) chloride) (50 μM) in sodium formate and in culture medium. Loss of compound 1 and formation of Co(II)(H₂ O)₆ ²⁺ and DCE (2) was determined by HPLC as described herein. The filled symbols represent deoxygenated solutions whereas the open symbols are equilibrated with air.

FIG. 2 shows the formation of DCE (2) by radiolysis of compound 1 in deoxygenated formate solution as demonstrated by HPLC/bioassay.

FIG. 3 shows the effect of radiolytic reduction of compound 3-(N,N-bis(2-chloroethyl)-N-methyl-N-[(1-methyl4-nitro-5-imidazolyl)methyl]ammonium chloride)) (50 μM) in sodium-formate. Loss of compound 3 and formation of the cytotoxic product 4 (HN2) was determined by HPLC as described herein.

FIG. 4 shows the increase in cytotoxicity of a solution of 3 (100 μM in αMEM culture medium) after irrradiation under anoxic conditions at a dose of 100 Gy as demonstrated by bioassay against UV4 cells in 96 well plates as described herein. The cytotoxicity of authentic 4 (HN2) is also shown.

FIG. 5 shows the radiation dose dependence of the cytotoxicity of solutions of 3 (100 μM in αMEM), and the estimated concentrations of the released cytotoxic effector (4, HN2), under aerobic (open symbols) or anoxic (filled symbols) conditions. Concentration of 4 in the irradiated solutions were calculated using the method described herein.

DESCRIPTION OF THE INVENTION

As defined above, this invention provides an approach to cancer therapy (radiation-activated cytotoxin therapy, RACT) in which ionising radiation is used to activate, by reduction, a RACP compound to form a more toxic species in a tumour. The mechanism of activation is believed to be as follows: ##STR12##

As can be seen, radiolysis of water generates three primary radical species (the aquated electron e_(aq) ⁻, the hydrogen radical H. and the hydroxyl radical OH.) of which e_(aq) ⁻ and H are strong reducing agents. These radiation-induced reductants are capable of reducing prodrugs of low reduction potential which are not substrates for enzymatic reduction and hence will not be activated outside the radiation field.

However, the yield of reducing species generated on the radiolysis of water is very low (corresponding to a total concentration of reductants equivalent to ca. 0.33 μmol/kg/Gy). This places an upper limit on the amounts of activated cytotoxin which can be generated by this mechanism, although if the OH. gives rise secondarily to reducing radicals (e.g. via abstraction of H. from saturated carbon atoms) this may raise the theoretical upper limit towards the total radical yield of 0.62 μmol/kg/Gy.

Therefore, in order to be clinically effective in the present method of treatment of neoplastic disease while avoiding the disadvantages associated with BD therapy, the RACP compound must fulfill a number of general criteria. These criteria are that it exhibit low toxicity to the patient unless activated by irradiation; that it be able to be reduced by reducing agents generated by the radiolysis of water (the aquated electron and/or the hydrogen radical and/or secondary reducing radicals derived from OH.); and that it releases, upon reduction, a sufficient amount of an effector. A high cytotoxic potency of the effector is possibly the most important of the general requirements, as it helps to compensate for what might be a low yield of effector release.

In addition to these general criteria, it is preferred that the RACP compound satisfy the further requirement of not being an efficient substrate for enzymatic reduction.

Examples of prodrugs which fulfill at least the three general criteria are the compounds of formulae I, VI, VII and VIII as defined above. Of these compounds, those of formulae I and VIII are novel, whereas the compounds of formulae VI and VII are known.

The known compounds of formula VI and VII can be prepared by any of the methods described for their preparation in the literature. For example, the known compounds of formula VII can be prepared by reacting the free base of N,N-bis(2-chloroethyl)-ethylenediamine with trans-Na[Co(Me-acac)₂ (NO₂)₂ ] (where Me-acac is 3-alkyl-pentane-2,4-dionato anion) in the presence of activated charcoal, followed by purification by cation-exchange chromatography [Ware, Palmer, Wilson and Denny, J. Med. Chem., 36: 1839-1846, 1993].

As a further example, the known compounds of formula VII can be prepared by treatment of the appropriate nitrobenzyl chlorides with N-methyldiethanolamine in CH₃ CN, followed by halogenation of the resulting quaternary diols with SOCl₂ at room temperature [Tercel, Wilson and Denny, J. Med. Chem. 36: 2578-2579, 1993; J. Med. Chem. 39: 1084-1094, 1996].

The novel compounds of the general formula I (in which R² is selected from formulae II-V) can be prepared by reacting the appropriate substituted halomethyl-substituted aromatic or heteroaromatic compounds directly with the appropriate tertiary aliphatic amines (for compounds of general formula I in which R² is of formulae IV and V), or by reacting the appropriate substituted aromatic or heteroaromatic aldehydes with the appropriate primary aliphatic amines, followed by reduction with sodium cyanoborohydride, and subsequent stepwise methylation, first with sodium cyanoborohydride/formaldehyde and then with an active methylating agent such as trimethyloxonium tetrafluoroborate (compounds of general formula I in which R² is of formulae II and III).

The method of Scheme 1 can be employed to prepare compounds of general formula I in which R² is of formulae II and III: ##STR13##

The typical method of Scheme 2 can be employed to prepare compounds of general formula I in which R² is of formula IV:

    __________________________________________________________________________     Scheme 2                                                                                                               #STR14##                                                                       #STR15##                                                                     no.                                                                               Z   Y Ar                              __________________________________________________________________________       15  17 H  NH.sub.2 H  Me                                                                                                      #STR16##                         - 16  19 H  NH.sub.2 H  Me                                                                                                   #STR17##                         - 18 NH.sub.2 Me                                                                                                             #STR18##                         - 20 NH.sub.2 Me                                                                                                             #STR19##                      Preparation of new chlorides ArCH.sub.2 Cl                                                                                      #STR20##                                                                       21 NH1##                                                                     .sub.2 Me                                                                        #STR22##                           22 NH.sub.2 Me                                                                                                             #STR23##                                                                       #STR24##                                                                       23 NH.sub.2 Me                                                                ##STR26##                      __________________________________________________________________________      i: Benzene or MeCN/reflux/10-100 h.                                            ii: tButyl 2,2dichloroacetate/KOtBu/DMF/10° C./1 h.                     iii: AcOH/reflux/1.5 h.                                                        iv: NaBH.sub.4 /MeOH/20° C./30 min.                                     v: MsCl/Et.sub.3 N/CH.sub.2 Cl.sub.2 /0° C./15 min.               

The typical method of Scheme 3 can be employed to prepare compounds of general formula I in which R² is of formula V: ##STR27##

The method of Scheme 4 can be employed generally to prepare the novel compounds of general formula VIII: ##STR28##

It will be appreciated that the starting material (shown as 47) in Scheme 4 can be varied depending on the desired values for Y, Z, n and m in the compound of formula VIII. Similarly, Cr(Meacac)₂ [(OH)₂ ]⁺ (prepared according to Abe, Y.; Shoji, M. Inorg. Chem. 1988, 27, 986) may be substituted for Co(Meacac)₃ as reagent, if a compound of formula VIII, in which T is Cr(III) is desired.

The RACP compounds for use in the therapeutic methods of the invention, whether compounds of formulae I, VI, VII or VIII, can be administered in any pharmaceutically appropriate form, such as orally administrable or injectable forms. Such forms can include conventional pharmaceutically acceptable vehicles, carriers or excipients.

In preferred embodiments of the invention, the RACP compounds are administered by injection. In this form of the invention, the administrable form of the RACP may comprise a sterile, reconstitutable, (lyophilised, water soluble) powder.

The clinical treatment schedule can be described as follows:

The RACP compounds would be administered to the patient at an appropriate dosage rate. The preferred dosage rate is expected to be in the range of about 0.01 to 100 mg/kg body weight of patient.

Any clinically-useful method of radiotherapy may be employed to activate the RACP in tumours. For example, conventional daily fractioned radiation (photons or electrons) may be used, in which case the tumour-bearing volume would be irradiated to a dose of about 2-2.5 Gy each day for a period of several weeks, to give a total dose in the order of 50 Gy. The RACP would be administered shortly before each radiation dose, at a timing such that the prodrug is at maximal concentration in the tumour at the time of irradiation.

It may be advantageous to use high dose rate radiation (achievable using electron beams) so that radiolytic consumption of oxygen is rapid enough to deplete residual oxygen in hypoxic regions, rendering these completely anoxic.

The present invention will now be described in relation to the following examples. It will however be understood by those persons skilled in the art that the examples given are illustrative only and are non-limiting.

EXAMPLE 1 Activation of a Cobalt(III)-nitrogen Mustard Complex of General Formula VI by Ionising Radiation

The cobalt(III)-nitrogen mustard compound 1 (an example of general formula VI) is a bioreductive drug which is selectively toxic to hypoxic mammaliam cells in culture (Ware, D. C., Palmer, B. D., Wilson, W. R and Denny, W. A. J. Med. Chem., 36, 1839-46, 1993; Wilson W. R, Moselen, J. W., Cliffe, S., Denny, W. A. and Ware, D. C. Int. J. Radiat. Oncol. Biol. Phys., 29, 323-327, 1994). The proposed mechanism of bioreductive activation, involving one-electron reduction to the corresponding Co(II) compound and dissociation of the latter to release and thereby activate the coordinated nitrogen mustard ligand DCE (2), is as follows: ##STR29##

The present example shows that reductive activation of compound 1 can be effected using ionising radiation rather than a biological reducing system.

A solution of compound 1 (50 μM in 0.1M sodium formate, 0.085 M sodium hydrogen phosphate, adjusted to pH 7.0 with 8.5% orthophosphoric acid) was deaerated by evacuation and irradiated using a cobalt-60 source at a dose rate of 50 Gy/min. The products were analysed by HPLC after derivatisation with 4-(2-pyridylazo)resorcinol to detect Co(II)(H₂ O)₆ ²⁺, and after derivatisation with diethyldithiocarbamate (DDC) to detect DCE. The loss of the parent complex and the formation of Co(II)(H₂ O)₆ ²⁺ and DCE is shown as a function of radiation dose in FIG. 1.

The initial gradient of these curves corresponds to that expected for a one-electron reduction (yield of reductants in formate buffer=0.62 μmol.L⁻¹.Gy⁻¹ ; thus one-electron reduction would require a radiation dose of 81 Gy in this experiment). The consumption of compound I and formation of DCE (2) and Co(II)(H₂ O)₆ ²⁺ in this system is inhibited by oxygen (FIG. 1). Release of DCE (2) and Co(II)(H₂ O)₆ ²⁺ from compound 1 by irradiation was also observed in culture medium (αMEM)(FIG. 1).

Bioassay experiments demonstrate that the cytotoxic activity in solutions of compound 1 is changed qualitatively and quantitatively by irradiation. A solution of compound 1 in sodium formate was irradiated to a dose corresponding to one reducing equivalent, and the products analysed by HPLC. The column eluate was bioassayed against log-phase UV4 cells growing in 96-well plates. The results show the loss of bioactivity in the region corresponding to the parent, and the appearance of a new peak of bioactivity corresponding in retention time to authentic DCE (FIG. 2).

EXAMPLE 2 Activation of a (nitroimidazolyl)methyl Quaternary Ammonium Nitrogen Mustard Derivative of General Formula VII by Ionising Radiation

The proposed mechanism of reductive activation of the (nitroimidazolyl)methyl quaternary ammonium nitrogen mustard (3) by ionising radiation, leading to release of mechlorethamine (4, HN2) as the cytotoxic species, is shown as follows: ##STR30##

The formation of 1,5-dimethyl-4-nitroimidazole and the dimer 5, which were also identified and quantitated, are properly markers for the proposed one-electron reduction route.

A solution of compound 3 (50 μM in 0.1 M sodium formate/0.085 sodium hydrogen phosphate, pH 7.0) was irradiated at a range of doses using a cobalt-60 source (ca. 40 Gy/min) under anoxic conditions, incubated with diethyldithiocarbamate (DDC) to derivatise any HN2 released, and analysed by HPLC (FIG. 3; values are mean and error bars are ranges for two independent experiments). Loss of compound 3 was observed, with an initial G value of approximately 0.72 μM/Gy, corresponding to a stoichiometry of 1.16 mol prodrug reduced/mol radiolytic reductants generated. An adduct between (4;HN2) and DDC was detected, its identity being confirmed by comparison (retention time and spectrum) with the authentic synthetic DDC-HN2 diadduct. The initial G value for HN2 formation was 0.76 μM/Gy, and the maximum yield (at a radiation dose corresponding to one reducing equivalent) was 91% of the initial prodrug concentration. Two other products consistent with the above scheme (1,5-dimethyl-4-nitroimdazole and the dimer 5) were identified by comparison with authentic compounds. The total yield of methylimidazolyl radicals accounted for by these products (twice the yield of 5 plus the yield of 1,5-dimethyl-4-nitroimidazole) was 40.6 μM (81%). The observation that the stoichiometry of prodrug loss and HN2 formation is slightly greater than unity is suggestive of a short radical chain reaction such as reduction of methylimidazolyl radicals by formate to generate CO2.⁻ radicals and 1,5-dimethyl-4-nitroimidazole. This interpretation was supported by separate experiments in which 3 was reduced by radiation in 0.1 M butanol/water, which gave 4 and 5 in high yield while 1,5-dimethyl-4-nitroimidazole was present in only trace amounts.

The increase in cytotoxicity of solutions of 3 as a result of irradiation under anoxic conditions is demonstrated in FIG. 4. In this experiment a solution of 3 (200 μM in αMEM) was deoxygenated by bubbling with 5% CO₂ /95% N₂ and irradiated with 4 MeV electrons using a linear accelerator (100 Gy). The solution was then titrated against log-phase UV4 cells in 96-well plates. The cells were exposed to the irradiated solution for 4 hr under aerobic conditions (CO₂ incubator, 37° C.). The wells were then washed with fresh medium and the cells were cultured for a further 4 days before determining cell density by staining with methylene blue. The cytotoxicity of the irradiated solution (apparent IC₅₀ 0.11 μM, based on the concentration of 3 prior to irradiation) was intermediate between that of unirradiated 3 (IC₅₀ 3.0 μM) and that of authentic 4 (IC₅₀ 0.055 μM). The change in apparent IC₅₀ with radiation dose in experiments of this type, and comparison with IC₅₀ values of the prodrug and effector, is shown in FIG. 5A.

A method is described below for estimating, from the apparent IC₅₀, the concentration of cytotoxic effector in irradiated prodrug solutions. Using this method, the concentration of HN2 in irradiated solutions of 3 (100 μM in αMEM) was estimated from the IC₅₀ values shown in FIG. 5A. These calculations indicate an approximately linear increase in apparent HN2 concentration with dose (FIG. 5B), with a G value for release of effector (G(+E)) of 0.32 μM/Gy under anoxic conditions. Irradiation in the presence of oxygen (continuous bubbling with 5% CO₂ /95% O₂ during irradiation) gave a G(+E) value of 0.013 μM/Gy, indicating effective inhibition by oxygen.

The nitrobenzyl quaternary ammonium nitrogen mustard analogues (6-10), (N,N-bis(2-chloroethyl-N-methyl-N-(2-nitrobenzyl)ammonium chloride, N,N-bis(2-chloroethyl-N-methyl-N-(3-nitrobenzyl)ammonium chloride, N,N-bis(2-chloroethyl-N-methyl-N-(4-nitrobenzyl)ammonium chloride, N,N-bis(2-chloroethyl-N-methyl-N-(4-methyl-sulfonyl)benzyl)ammnonium chloride, and N,N-bis(2-chloroethyl-N-methyl-N-benzylammonium chloride, respectively) some of which are known bioreductive drugs with selective toxicity for hypoxic cells in culture (Tercel, M., Wilson, W. R. and Denny, J. Med. Chem., 36, 2578-2579, 1993; Denny, W. A., Wilson, W. R., Tercel, M., van Zijl, P. and Pullen, S. M. Int. J. Radiat. Oncol. Biol. Phys., 29, 317-321, 1994), also release 4 on exposure to ionising radiation.

EXAMPLE 3 Demonstration of Radiolytic Release of Cytotoxic Effectors from a Variety of Compounds of Formulae I, VI, VII and VIII

The above methods have been used to demonstrate release of cytotoxic effectors on irradiation of solutions of the compounds shown in Table 1. Two different assays were used.

Assay 1: Irradiation of the prodrug (50 μM) in formate buffer, with analysis of products by HPLC.

The prodrug, was dissolved in water (typically to approximately 2 mM) and the concentration determined by spectrophotometry. This stock solution was diluted to a final concentration of 50 μM in 0.1 M sodium formate, 0.085 M, Na₂ HPO₄ (adjusted to pH 7.0 with 8.5% orthophosphoric acid). A sample of 5 or 10 ml was evacuated in a glass tube and irradiated with a gamma source (cobalt-60, dose rate 40-50 Gy/min) to a range of total doses (typically 20.25, 40.5, 60.75, 81, 162 and 243 Gy). Immediately after irradiation, air was introduced and the sample was analysed by HPLC. The aliphatic mustard effectors 2 (DCE) and 4 (HN2) were derivatised with diethyldithiocarbamate (DDC) prior to HPLC by adding DDC from a stock solution at 100 mM in water (prepared freshly) to give a final concentration of 2.5 mM. Samples were incubated at 37° C. for 30 min (4) or 90 min (2). In the case of 4, an equal vol MeOH was then added to redissolve the product. HPLC analysis used a Waters C18 μbondapak column (8×100 mm) with a mobile phase comprising suitable linear gradients of MeCN in 0.45 M ammonium formate, pH 4.5 (flow rate 1.8 ml/min). Detection was by diode array absorbance (Hewlett Packard 1040A). Authentic synthetic standards of each effector were used as the basis for identification (retention time and spectrum) and quantitation. The G value for formation of effector, G(+E), was calculated from the initial slope of the plot of effector concentration versus radiation dose. The effectors 12, 37 (DACA) and 46 (AMAC) were sufficiently stable to be detected directly by HPLC, without derivatisation. FIGS. 1 and 3 illustrate results of this assay. ##STR31##

Assay 2: Irradiation of the prodrug in tissue culture medium (αMEM), with bioassay of the irradiated solution against UV4 cells.

A solution of prodrug was prepared in culture medium (αMEM), without use of organic solvents, and sterilised by filtration. The prodrug concentration in this solution was determined by spectrophotometry or HPLC. Samples (0.5 ml) in small glass test tubes were gassed vigorously (to cause turbulent mixing) with hurmidified 5% CO₂ /95% N₂ or 5% CO₂ /95% O₂ for 5 min (200 ml/min), using an 18 gauge needle through a rubber septum. Immediately after withdrawing the needle the sample was irradiated (4 MeV electrons, using a linear accelerator) to the required dose, using a charge collection plate (calibrated against the Fricke dosimeter) to determine the actual dose delivered. For experiments using 95% O₂, gassing was continued during irradiation to minimize radiolytic oxygen consumption. In most experiments the dose/pulse was approximately 3 Gy, and the pulse frequency was approximately 30 per min. Irradiated samples were transferred to cryogenic vials and frozen in liquid nitrogen within 45 seconds of the end of irradiation. These samples were stored at -80° C. until bioassay.

The bioassay was performed using log-phase cultures of UV4 cells in 96-well plates, seeded 24 hr previously (300 cells in 50 μl αMEM containing 5% foetal calf serum per well). The drug sample was thawed rapidly in a 37° C. waterbath, foetal calf serum added to a final concentration of 5%, diluted if necessary, and titrated across the 96-well plate using serial 2 or 3-fold dilutions in duplicate or triplicate. The elapsed time between thawing and titrating was <10 min. Plates were incubated at 37° C. for 4 hr under aerobic conditions (5% CO₂ incubator), the wells were washed three times with fresh medium and the cells grown for a further 4 days in 150 μl αMEM with 5% FCS. Cells were stained with methylene blue or suphorhodamine B, and absorbances determined with a plate reader. The IC₅₀ value was calculated as the drug concentration required to lower the absorbance to 50% of that of controls on the same plate. The IC₅₀ of irradiated solutions was expressed with respect to the starting concentration of the prodrug. (E.g. if the IC₅₀ of the unirradiated prodrug was 10 μM, and the apparent cytotoxicity was increased by a factor of 10 after irradiation, the resulting IC₅₀ was descnrbed as 1 μM).

The following controls were included in each bioassay experiment:

1. Prodrug freshly dissolved, or diluted from frozen stock solution, immediately before bioassay.

2. Unirradiated prodrug which had been gassed and processed (frozen and thawed) as for the irradiated samples.

3. Effector freshly dissolved, or diluted from a frozen stock solution in which it is known to be stable, immediately before bioassay.

4. Effector diluted into αMEM and immediately frozen in liquid N₂.

There was no consistent difference between controls 1 and 2, or 3 and 4, for any of the compounds tested indicating that there was no significant compound loss during freezing and thawing, and that there was no significant non-radiolytic activation in formate buffer.

The concentration of effector in the irradiated drug solutions, [E], was calculated from the apparent IC₅₀ of the irradiated mixture, IC₅₀,M (where the concentration is expressed with respect to the intitial concentration of prodrug) using the following relationship: ##EQU1## where IC₅₀,E is the IC₅₀ value of the authentic effector IC₅₀,P is the IC₅₀ of (unirradiated) prodrug

and [P_(o) ] is the initial concentration of the prodrug in the irradiated solution.

The derivation of the above relationship makes the assumption that the cytotoxicity of the effector is not modified by the prodrug, and that when the toxicity of the prodrug itself is significant (as will be the case at low radiation doses when only a small percentage conversion of prodrug to effector has occurred) then the combined toxicity is additive. In particular, we assume that the prodrug concentration can be expressed as an equivalent concentration of effector. The above equation also assumes that the stoichiometry of effector formation (mol effector formed/mol prodrug reduced) is unity. FIG. 5 demonstrates the use of the above equation to estimate effector yields.

Interpretation of Assays

The above assays give different information. Assay 1 establishes whether the intended effector is released from the prodrug when the latter is reduced by radiation. Assay 2 examines to what extent the cytotoxicity of the prodrug solution is increased following irradiation. This will depend on the efficiency of effector release from the reduced prodrug (as measured by Assay 1), but also on the efficiency of prodrug reduction by radiation in the presence of scavenging species in culture medium, and on the difference in cytotoxic potency between the prodrug and effector.

In assay 2, the concentration of cytotoxic effector in irradiated solutions can be calculated from the measured IC₅₀ of the solution, provided that certain assumptions are met (see above), and the G value for release of effector (G(+E); can therefore be calculated. However, it should be noted that even if the efficiency of prodrug reduction is undiminished by competing electron acceptors in medium, the G value is expected to be lower in medium than in formate where oxidising OH. radicals are quantitatively converted to reducing CO₂.⁻ radicals. Since OH represents approximately half the primary radical yield in water, the theoretical yield of radiolytcally-generated reductants in medium is approximately half that in formate (unless OH. gives rise to reducing radicals on reaction with constituents in medium).

In identifying preferred RACP, we seek compounds with high values of G(+E) and low values of IC₅₀,E. Ideally, radiolytic activation of the prodrug, using a clinially relevant radiation dose of 2 Gy, should provide an effector concentration which is large relative to IC₅₀,E. We thus evaluate the ratio R₂ where

    R.sub.2 =[E].sub.2 /(IC.sub.50,E)

and [E]₂ is the effector concentration at 2 Gy, calculated from G(+E).

We note that G(+E) is not likely to be independent of prodrug concentration when scavengers are present since the ability of the prodrug to capture reducing equivalents competitively is then expected to increase with prodrug concentration. Thus if two prodrugs release the same effector, by the same mechanism, but have different IC₅₀ values (without irradiation), the less toxic analogue would allow use of higher prodrug concentrations in a biological system and would be expected to provide a higher G(+E) in cells as well as a higher prodrug/effector toxicity differential. Thus, in addition to seeking prodrugs with high values of R₂, we also seek prodrugs with high values of IC₅₀,P.

Results

The results for the above two assays are summarised in Table 1. IC₅₀ values for prodrugs and effectors were determined against the UV4 and SKOV3 cell lines. The UV4 cell line is hypersensitive to DNA alkylating agents (Hoy et al., Mutation Research, 130: 321-332, (1984)), while the SKOV3 cell line (derived from a human ovarian carcinoma) is considered more representative in its sensitivity. The most important screening parameters are therefore IC₅₀,P and R₂ for the SKOV3 cell line.

                                      TABLE 1                                      __________________________________________________________________________     Reductive activation of prodrugs by radiation: summary of yields of            effectors, and cytotoxicity                                                      data for prodrugs and effectors.                                                       G(+E).sup.c, anoxic,                                                   μM/Gy UV4                                                                           Assay      IC.sub.50, P.sup.f                                                                   IC.sub.50, E.sup.g                                                                       SKOV3                                     Cmpd                                                                               Effector.sup.a                                                                       1.sup.d                                                                            Assay 2.sup.c                                                                         (μM)                                                                              (μM)                                                                               R.sub.2.sup.h                                                                     IC.sub.50, P(μM)                                                                  IC.sub.50, E(μM)                                                                   R.sub.2                      __________________________________________________________________________     11  12.sup.b                                                                             0.38.sup.i 1135 ± 122                                                                        15 ± 6                                             15 37: 0.072 0.067(150) >150 0.49 ± 0.11 0.27 >150 3.4 ± 0.8                                                             0.039                           DACA.sup.b                                                                    16 37.sup.b 0.19 0.13(167) 40 ± 8 0.49 ± 0.11 0.53 169 ± 58                                                           3.4 ± 0.8 0.076                                                              17 38:AMAC.sup.b 0.034                                                        0.03 ± 0.01(5) 0.78                                                         ± 0.09 0.011 ±                                                           .001 5.5 4.0 ± 0.1                                                          0.046 ± .002 1.3                                                             18 38  0.0025(15) 3.1                                                         ± 0.7 0.011 ±                                                            .001 0.45                      19 38  0.020(15) 0.16 ± 0.03 0.011 ± .001 3.6                            21 38  0.04(15) 2.0 ± 0.4 0.011 ± .001 7.3                               20 38  0.006(15) 1.0 ± 0.3 0.011 ± .001 1.1                              22 38  0.06(15) 1.9 ± 0.4 0.011 ± .001 11                                27 46:AQ4  0.0056 ± 0.27 ± 0.04 0.0021 ± 0.007 5.3 9.7 ±                                                           0.03 0.074 ± 0.0004                                                         0.15                              0.0008(1.6)                                                                 1 2:DCE.sup.b 0.76 0.15(50) 0.30 ± 0.1 0.036 ± .004 8.3 20 ± 7                                                        2.4 ± 0.3 0.12                                                               28 47:DACA- 0.8  31                                                           ± 10 1.6 ± 0.4                                                           74 ± 17 1.6 ± 0.3         EN.sup.b                                                                      6 4:HN2.sup.b 0.26 0.114 ± .018 61 ± 14 0.034 ± .008 6.7                                                              10,080 ± 1.09 ±                                                          .04 0.21                          (200)    3600                                                               7 4.sup.b 0.045                                                                8 4.sup.b 0.20 0.04(150) 35 0.034 ± .008 2.4                                9 4.sup.b 0.19 0.068(400)                                                      10 4.sup.b 0.05                                                                3 4.sup.b 0.74, 0.26(20) 1.6 ± 0.3 0.034 ± .008 15 143 ± 25                                                           1.09 ± .04 0.48                                                                0.76 0.34(100)   20                                                          0.62                             0.43 ± 0.03   25   0.79                                                     (200)                                                                     __________________________________________________________________________      Footnotes:                                                                     .sup.a Structural formulae shown in FIGS. 1-3 and Schemes 1-4.                 .sup.b The identity of the indicated effector was confirmed as a product       of radiolysis in formate buffer (assay I) by comparison of HPLC retention      time and absorbance spectrum with that of authentic (synthetic) standard       .sup.c Yield of effector                                                       .sup.d Assay 1: Radiolytic reduction in sodium formate, with analysis of       effector formation by HPLC. See text for details. Where two values are         shown, these are from independent experiments                                  .sup.e Assay 2: Radiolytic reduction in αMEM, with effector              formation estimated by bioassay against UV4 cells. See text for details.       When errors are shown, the values are the mean and sem for independent         experiments. (Repeat bioassay of the same irradiated solution does not         count as a separate experiment). Values in parenthesis are the                 concentration of prodrug in the irradiated solution.                           .sup.f IC.sub.50 of the unirradiated prodrug against the indicated cell        line. 4 hr drug exposure under aerobic conditions. Values are mean ±        SEM for independent experiments.                                               .sup.g IC.sub.50 of the authentic effector (identified in column 2)            against the indicated cell line. 4 hr drug exposure under aerobic              conditions. Values are mean ± SEM for independent experiments.              .sup.h [E].sub.2 /(IC.sub.50, E), where [E].sub.2 is the effector              concentration at 2 Gy, calculated from G(+E) in αMEM (assay 2)           .sup.i Irradiated at one dose only (81 Gy).                              

EXAMPLE 4a Preparation of 3-(chloromethyl)-6-[N,N-dimethyl-N-(4-nitrobenzyl)-ammonio]-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]indoline chloride (compound 13) of General Formula I by the Method Outlined in Scheme 1

A mixture of 6-amino-3-(chloromethyl)-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]-indoline (32) [for preparation, see Example 8] (464 mg, 1.12 mmol), 4-nitrobenzaldehyde (202 mg, 1.34 mmol) and toluenesulfonic acid monohydrate (21 mg, 0.1 mmol) in benzene (30 mL) was heated to reflux and most of the benzene distilled off over 15 min. The remaining mixture was evaporated to dryness and the residue dissolved in THF (30 mL) and MeOH (10 mL). Sodium cyanoborohydride (0.14 g, 2.23 mmol) then 2 N HCl (0.3 mL) were added and the mixture stirred at 20° C. for 25 min, then evaporated. The residue was diluted with aq. NaCl, extracted with EtOAc (×2), and the extracts were dried (Na₂ SO₄) and evaporated. Dry column chromatography, eluting with EtOAc/petroleum ether (2:3), gave, 3-(chloromethyl)-6-[N-(4-nitrobenzyl)amino]-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]indoline (33) as a yellow-orange oil (545 mg, 89%). ¹ H NMR (CDCl₃) δ 9.56 (s, 1 H, indole NH), 8.15 (d, J=8.7 Hz, 2 H, ArH o to NO₂), 7.77 (d, J=1.8 Hz, 1 H, H-7), 7.50 (d, J=8.7 Hz, 2 H, ArH m to NO₂), 7.02 (d, J=8.2 Hz, 1 H, H-4), 6.94 (d, J=2.4 Hz, 1 H, H-3'), 6.85 (s, 1 H, H-4'), 6.26 (dd, J=8.2, 2.2 Hz, 1 H, H-5), 4.63-4.56 (m, 1 H, H-2), 4.48 (s, 2 H, NCH₂ Ar), 4.42 (dd, J=10.8, 4.2 Hz, 1 H, H-2), 4.05 (s, 3 H, OCH₃), 3.93 (s, 3 H, OCH₃), 3.90 (s, 3 H, OCH₃), 3.78-3.69 (m, 2 H, CHCH₂ Cl), 3.54-3.46 (m, 1 H, CHCH₂ Cl); ¹³ C NMR δ 160.3 (CO), 150.1, 148.3, 147.2, 147.1, 144.8, 140.5, 138.8, 129.9, 125.5, 123.6, 120.6 (aromatic C), 127.7, 123.8 (o,m to NO₂), 124.7, 108.5, 106.4, 103.1, 97.6 (C-4,5,7,3',4'), 61.5, 61.1, 56.2 (3×OCH₃), 54.8 (C-2), 47.5, 47.3 (CH₂ Cl, NCH₂ Ar), 43.1 (C-3). MS (DEI, ³⁵ Cl) m/z 550 (50%, M⁺), 234 (100%); HRMS (FAB) calcd. for C₂₈ H₂₇ ClN₄ O₆ (M+H) 551.1697, found 551.1690.

Sodium cyanoborohydride (0.12 g, 1.9 mmol) then 2 N HCl (1.0 mL) were added to a solution of the above indoline (33) (545 mg, 0.96 mmol) and formaldehyde (0.87 mL of a 40% w/v aq. solution, 12 mmol) in THF (20 mL) and MeOH (15 mL) and the mixture stirred at 20° C. for 50 min. The mixture was diluted with aq. NaHCO₃, extracted with EtOAc (×2), and the extracts dried (Na₂ SO₄) and evaporated. Dry column chromatography on silica gel, eluting with EtOAc/petroleum ether (2:3), gave 3-(chloromethyl)-6-[N-methyl-N-(4-nitrobenzyl)amino]-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]indoline (34) as a yellow-orange oil (348 mg, 62%).

A sample was crystallised from EtOAc-Et₂ O as yellow needles, mp 178-179° C. ¹ H NMR (CDCl₃) δ 9.46 (s, 1 H, indole NH), 8.16 (d, J=8.7 Hz, 2 H, ArH o to NO₂), 7.88 (d, J=1.7 Hz, 1 H, H-7), 7.39 (d, J=8.7 Hz, 2 H, ArH m to NO₂), 7.09 (d, J=8.4 Hz, 1 H, H-4), 6.95 (d, J=2.3 Hz, 1 H, H-3'), 6.86 (s, 1 H, H-4'), 6.41 (dd, J=8.4, 2.5 Hz, 1 H, H-5), 4.66 (s, 2 H, NCH₂ Ar), 4.61 (dd, J=10.8, 8.7 Hz, 1 H, H-2), 4.44 (dd, J=10.8, 4.2 Hz, 1 H, H-2), 4.04 (s, 3 H, OCH₃), 3.93 (s, 3 H, OCH₃), 3.90 (s, 3 H, OCH₃), 3.81-3.72 (m, 2 H, CHCH₂ Cl), 3.56-3.48 (m, 1 H, CHCH₂ Cl), 3.11 (s, 3 H, NCH₃); ¹³ C NMR δ 160.3 (CO), 150.1, 150.0, 147.1, 146.8, 145.0, 140.5, 138.8, 129.9, 125.5, 123.6, 119.8 (aromatic C), 127.4, 123.9 (o,m to NO₂), 124.6, 108.4, 106.5, 102.4, 97.6 (C-4,5,7,3',4'), 61.5, 61.1, 56.3 (3×OCH₃), 56.6 (NCH₂ Ar), 54.9 (C-2), 47.3 (CH₂ Cl), 43.0 (C-3), 39.3 (NCH₃). Anal. Calculated for C₂₉ H₂₉ ClN₄ O₆ : C, 61.7; H, 5.2; N, 9.9. Found: C, 61.9; H, 5.4; N, 9.8%.

Methyl trifluoromethanesulfonate (0.21 mL, 1.9 mmol) and 2,6-di-t-butylpyridine (0.42 mL, 1.9 mmol) were added to a solution of the above indoline (34) (352 mg, 0.62 mmol) in dry CH₂ Cl₂ (6 mL) and the mixture allowed to stand at 20° C. for 3 days, then evaporated. The residue was dissolved in CH₂ Cl₂, washed with water (×2), dried (Na₂ SO₄), and evaporated. Trituration with Et₂ O (×5) removed all of the remaiing di-t-butylpyridine. The resulting pale yellow powder was dissolved in MeOH (5 mL) and water (2.5 mL) and passed through a column of Biorad AG 1-X4 ion exchange resin in the chloride form (10 g), eluting with MeOH-H₂ O (2:1, 20 mL). The eluate was evaporated, the residue dissolved in CH₂ Cl₂, dried (Na₂ SO₄), and evaporated. Trituration with EtOAc-Et₂ O then EtOAc-CH₂ Cl₂ gave 3-(chloromethyl)-6-[N,N-dimethyl-N-(4-nitroberzyl)-ammonio]-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]indoline chloride (compound 13) as a pale yellow solid (126 mg, 33%), mp 124-125° C. ¹ H NMR [(CD₃)₂ SO] δ 11.56 (d, J=1.7 Hz, 1 H, indole NH), 8.53 (s, 1 H, H-7), 8.20 (d, J=8.8 Hz, 2 H, ArH o to NO₂), 7.70 (s, 2 H, H-4,5), 7.48 (d, J=8.8 Hz, 2 H, ArH m to NO₂), 7.12 (d, J=2.1 Hz, 1 H, H-3'), 6.96 (s, 1 H, H-4'), 5.29 (s, 2 H, NCH₂ Ar), 4.82-4.74 (m, 1 H, H-2), 4.41 (dd, J=10.8, 4.4 Hz, 1 H, H-2), 4.12-4.02 (m, 3 H, CHCH₂ Cl), 3.92 (s, 3 H, OCH₃), 3.82 (s, 3 H, OCH₃), 3.79 (s, 3 H, OCH₃), 3.68 (s, 6 H, NMe₂); ¹³ C NMR δ 160.6 (CO), 149.2, 148.4, 145.0, 144.2, 140.2, 139.0, 135.1, 134.5, 130.0, 129.9, 123.1 (aromatic C), 134.0, 123.4 (o,m to NO₂), 125.7, 117.2, 109.7, 106.9, 98.0 (C-4,5,7,3',4'), 70.1 (NCH₂ Ar), 61.0, 60.9, 55.9 (3×OCH₃), 54.3 (C-2), 53.1, 52.8 (NMe₂), 47.3 (CH₂ Cl), 41.5 (C-3). Anal. Calculated for C₃₀ H₃₂ Cl₂ N₄ O₆.H₂ O: C, 56.9; H, 5.4; N, 8.8. Found: C, 57.2; H, 5.4; N, 8.9%.

EXAMPLE 4b Preparation of 3-(chloromethyl)-6-[N,N-dimethyl-N-(2-nitrobenzyl)-ammonio]-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]indoline chloride (compound 14) of General Formula I by the Method Outlined in Scheme 1

Similar reaction of (32) and 2-nitrobenzaldehyde gave 3-(chloromethyl)-6-[N-(2-nitrobenzyl)amino]-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]indoline (35) as a yellow oil (72%). ¹ H NMR (CDCl₃) δ 9.45 (s, 1 H, indole NH), 8.07 (dd, J=8.2, 1.2 Hz, 1 H, ArH o to NO₂), 7.78 (d, J=1.8 Hz, 1 H, H-7), 7.68 (dd, J=7.7, 0.9 Hz, 1 H, ArH), 7.57 (td, J=7.5, 1.3 Hz, 1 H, ArH), 7.41 (td, J=7.7, 1.4 Hz, 1 H, ArH), 7.00 (d, J=8.3 Hz, 1 H, H-4), 6.94 (d, J=2.4 Hz, 1 H, H-3'), 6.85 (s, 1 H, H-4'), 6.23 (dd, J=8.3, 2.2 Hz, 1 H, H-5), 4.75 (s, 2 H, NCH₂ Ar), 4.62-4.55 (m, 1 H, H-2), 4.42 (dd, J=10.7, 4.2 Hz, 1 H, H-2), 4.07 (s, 3 H, OCH₃), 3.94 (s, 3 H, OCH₃), 3.90 (s, 3 H, OCH₃), 3.78-3.68 (m, 2 H, CHCH₂ Cl), 3.53-3.44 (m, 1 H, CHCH₂ Cl); ¹³ C NMR δ 160.2 (CO), 150.1, 148.4, 148.2, 144.8, 140.5, 138.8, 135.4, 129.9, 125.4, 123.6, 120.5 (aromatic C), 133.7, 130.0, 128.1, 125.2, 124.7, 108.3, 106.4, 103.1, 97.6 (aromatic CH), 61.5, 61.1, 56.3 (3×OCH₃), 54.8 (C-2), 47.3 (CH₂ Cl), 45.8 (NCH₂ Ar), 43.1 (C-3). MS (DEI, ³⁵ Cl) m/z 550 (50%, M⁺), 234 (100%); HRMS (FAB) calcd. for C₂₈ H₂₇ ClN₄ O₆ (M+H) 551.1697, found 551.1690.

Reaction of the above indoline (35) with sodium cyanoborohydride and formaldehyde as above gave 3-(chloromethyl)-6-[N-methyl-N-(2-nitrobenzyl)amino]-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]indoline (36) as an orange oil (72%). ¹ H NMR (CDCl₃) δ 9.41 (s, 1 H, indole NH), 8.14 (dd, J=8.1, 1.2 Hz, 1 H, ArH o to NO₂), 7.88 (d, J=2.0 Hz, 1 H, H-7), 7.56 (td, J=7.5, 1.2 Hz, 1 H, ArH p to NO₂), 7.45-7.67 (m, 2 H, ArH), 7.06 (d, J=8.4 Hz, 1 H, H-4), 6.95 (d, J=2.3 Hz, 1 H, H-3'), 6.86 (s, 1 H, H-4'), 6.32 (dd, J=8.4, 2.5 Hz, 1 H, H-5), 4.95 (s, 2 H, NCH₂ Ar), 4.61 (dd, J=10.8, 8.7 Hz, 1 H, H-2), 4.44 (dd, J=10.8, 4.2 Hz, 1 H, H-2), 4.05 (s, 3 H, OCH₃), 3.93 (s, 3 H, OCH₃), 3.90 (s, 3 H, OCH₃), 3.80-3.72 (m, 2 H, CHCH₂ Cl), 3.55-3.47 (m, 1 H, CHCH₂ Cl), 3.12 (s, 3 H, NCH₃); ¹³ C NMR δ 165.8 (CO), 150.1, 150.0, 148.1, 145.0, 141.0, 140.5, 138.8, 135.1, 129.9, 123.6, 119.5 (aromatic C), 133.9, 128.5, 127.8, 125.5, 124.6, 108.1, 106.4, 101.9, 97.6 (aromatic CH), 61.5, 61.1, 56.3 (3×OCH₃), 55.2, 54.9 (NCH₂ Ar, C-2), 47.3 (CH₂ Cl), 43.1 (C-3), 39.1 (NCH₃). MS (DEI, ³⁵ Cl) m/z 564 (30%, M⁺), 429 (60%, M- C₇ H₅ NO₂), 234 (100%); HRMS calcd. for C₂₉ H₂₉ ClN₄ O₆ 564.17756, found 564.17897.

Reaction of the above indoline (36) with methyl trifluoromethanesulfonate and 2,6-di-t-butylpyridine as above, and ion exchange chromatography, followed by trituration with hot CH₂ Cl₂, gave 3-(chloromethyl)-6-[N,N-dimethyl-N-(2-nitrobenzyl)ammonio]-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]indoline chloride (compound 14) as an off-white solid (28%), mp 105-106° C. ¹ H NMR [(CD₃)₂ SO] δ 11.56 (d, J=2 Hz, 1 H, indole NH), 8.52 (s, 1 H, H-7), 7.98-7.93 (m, 1 H, ArH), 7.79-7.74 (m, 2 H, ArH), 7.62 (d, J=8.6 Hz, 1 H, H-4), 7.52-7.47 (m, 2 H, ArH), 7.11 (d, J=2.1 Hz, 1 H, H-3'), 6.96 (s, 1 H, H-4'), 5.44 (s, 2 H, NCH₂ Ar), 4.76 (dd, J=10.4, 9.4 Hz, 1 H, H-2), 4.41 (dd, J=10.8, 4.6 Hz, 1 H, H-2), 4.09-3.96 (m, 3 H, CHCH₂ Cl), 3.91 (s, 3 H, OCH₃), 3.82 (s, 3 H, OCH₃), 3.79 (s, 3 H, OCH₃), 3.67 (s, 6 H, NMe₂). Anal. Calculated for C₃₀ H₃₂ Cl₂ N₄ O₆.3H₂ O: 53.6; H, 5.7; N, 8.4. Found: C, 54.1; H, 5.5; N, 8.3%.

EXAMPLE 4c Preparation of 3-(chloromethyl)-6-[N,N-dimethyl-N-(4-nitrobenzyl)-ammonio]-1-(methanesulfonyl)indoline chloride (compound 11) of General Formula I by the Method Outlined in Scheme 1.

A mixture of 6-amino-3-(chloromethyl)-1-(methanesulfonyl)indoline (29) [Tercel, M., Denny, W. A. and Wilson, W. R., Bioorg. Med. Chem. Lett., 1996, in press] (73 mg, 0.28 mmol), 4-nitrobenzaldehyde (51 mg, 0.34 mmol) and toluenesulfonic acid monohydrate (5 mg, 0.3 mmol) in benzene (30 mL) was heated to reflux and most of the benzene slowly distilled off over 40 min. The remaining orange-brown solution was cyanoborohydride (35 mg, 0.56 mmol) then 2N HCl (0.5 mL) were added and the mixture was stirred at 20 C for 40 min, then evaporated. The residue was diluted with water, extracted with EtOAc (×2), and the extracts dried (Na₂ SO₄) and evaporated. Dry column chromatography, eluting with EtOAc/petroleum ether (1:2), gave 3-(chloromethyl)-1-(methanesulfonyl)-6-[(4-nitrobenzyl)amino]indoline (30) as a yellow oil (96 mg, 87%). ¹ H NMR (CDCl₃) a 8.19 (d, J=8.8 Hz, 2 H, ArH o to NO₂), 7.52 (d, J=8.8 Hz, 2 H, ArH m to NO₂), 7.00 (d, J=8.2 Hz, 1 H, H-4), 6.73 (d, J=2.2 Hz, 1 H, H-7), 6.22 (dd, J=8.2, 2.2 Hz, 1 H, H-5), 4.47 (s, 2 H, NCH₂ Ar), 4.03 (dd, J=10.8, 8.8 Hz, 1 H, CHHN), 3.92 (dd, J=10.8, 4.6 Hz, 1 H, CHHN), 3.69 (dd, J=10.4, 4.1 Hz, 1 H, CHHCl), 3.67-3.60 (m, 1 H, H-3), 3.53 (dd, J=10.4, 7.9 Hz, 1 H, CHHCl), 2.83 (s, 3 H, NSO₂ CH₃). ¹³ C NMR a 148.7, 147.2, 146.8, 143.4, 119.9 (C-6,8,9,1,4), 127.8, 123.9 (C-2 and 6, 3 and 5), 125.7, 107.9, 98.6 (C-4,5,7), 54.6 (C-2), 47.5, 46.8 (CH₂ Cl, NCH₂ Ar), 41.9 (C-3), 34.5 (SO₂ CH₃). MS (DEI, ³⁵ Cl) m/z 395 (35%, M⁺), 346 (100%, M-CH₂ Cl); HRMS calcd. for C₁₇ H₁₈ ClN₃ O₄ S 395.07066, found 395.06880.

Sodium cyanoborohydnide (40 mg, 0.64 mmol) then 2N HCl (0.5 mL) were added to a solution of 30 (96 mg, 0.24 mmol) and formaldehyde (0.18 mL of a 40% w/v aq. solution, 2.4 mmol) in MeOH (15 mL) and THF (5 mL) and the mixture stirred at 20° C. for 45 min. The solvent was evaporated, the residue was diluted with water and extracted with CH₂ Cl₂ (×2), and the extracts dried (Na₂ SO₄) and evaporated. Dry column chromatography (eluting with 1:2 EtOAc:petroleum ether) gave 3-(chloromethyl)-1-(methanesulfonyl)-6-[N-methyl-N-(4-nitrobenzyl)amino]indoline (31) (73 mg, 73%), mp (benzene-petroleum ether) 138-139 C. ¹ H NMR (CDCl₃) a 8.18 (d, J=8.8 Hz, 2 H, ArH o to NO₂), 7.39 (d, J=8.8 Hz, 2 H, ArH m to NO₂), 7.05 (d, J=8.4 Hz, 1 H, H-4), 6.82 (d, J=2.4 Hz, 1 H, H-7), 6.3 5 (dd, J=8.4 2.4 Hz, 1 H, H-5), 4.63 (s, 2 H, NCH₂ Ar), 4.04 (dd, J=10.8, 8.8 Hz, 1 H, CHHN), 3.93 (dd, J=10.8, 4.7 Hz, 1 H, CHHN), 3.71 (dd, J=10.4, 4.1 Hz, 1 H, CHHCl), 3.68-3.61 (m, 1 H, H-3), 3.55 (dd, J=10.4, 7.8 Hz, 1 H, CHHCl), 3.11 (s, 3 H, NCH₃), 2.81 (s, 3 H, NSO₂ CH₃). ¹³ C NMR a 150.3, 147.1, 146.5, 143.5, 118.9 (C-6,8,9,1,4), 127.4, 123.9 (C-2 and 6, 3 and 5), 125.5, 107.7, 97.9 (C-4,5,7), 56.5, 54.7 (C-2, NCH₂ Ar), 46.9 (CH₂ Cl), 41.8 (C-3), 39.5 (NCH₃), 34.5 (SO₂ CH₃). Anal. Calculated for C₁₈ H₂₀ ClN₃ O₄ S): C, 52.8; H, 4.9; N, 10.3; Cl, 8.7. Found: C, 52.6; H 5.1; N, 10.1; Cl, 8.9%.

A mixture of 31 (79 mg, 0.19 mmol) and trimethyloxonium tetrafluoroborate (105 mg, 0.71 mmol) in CH₂ Cl₂ (5 mL) was stoppered and stirred at 20 C for 4 days. Water was added and the mixture stirred until most of the oily solid dissolved. The separated organic layer was dried (Na₂ SO₄) and evaporated, dry column chromatography, eluting with EtOAc/petroleum ether (1:2), gave recovered starting material (24 mg, 30%). The aqueous phase was combined with the remaining oily solid, evaporated, and the residue extracted with MeOH. The resulting crude ammonium salt was converted to the chloride form by ion exchange chromatography on Dowex 50 WX8 resin (1.5 mL), loading the sample in MeOH:water (1:1) and washing until the eluate was neutral, then eluting with 1:1 MeOH:2N HCl (10 mL) followed by MeOH\4N HCl (1:1) (10 mL). The combined eluate was evaporated to give 3-(chloromethyl)-6-[N,N-dimethyl-N-(4-nitrobenzyl)-ammonio]-1-(methanesulfonyl)indoline chloride (11) as a white foam (87 mg). ¹ H NMR (CD₃ OD) a 8.17 (d, J=8.2 Hz, 2 H, ArH), 7.63 (br d, J=8.3 Hz, 1 H, H-4 or 5), 7.57 (br d, J=8.3 Hz, 1 H, H-4 or 5), 7.51 (s, 1 H, H-7), 7.41 (d, J=8.2 Hz, 2 H, ArH), 5.22 (s, 2 H, NCH₂ Ar), 4.32-4.25 (m, 1 H), 4.06-4.01 (m, 2 H), 3.96-3.93 (m, 2 H), 3.75 (s, 6 H, NMe₂), 3.02 (s, 3 H, NSO₂ CH₃). ¹³ C NMR a 150.7, 146.0, 145.8, 136.1, 135.7 (C-6,8,9,1,4), 135.3, 124.8 (C-2 and 6, 3 and 5), 128.2, 117.9, 107.6 (C-4,5,7), 73.1 (NCH₂ Ar), 55.3 (C-2), 54.6 (NMe₂), 47.8 (CH₂ Cl), 42.8 (C-3), 36.4 (SO₂ CH₃).

EXAMPLE 5a Preparation of 2-[N-(acridin-4-yl)carbonyl]aminoethyl-(dimethyl)-4-nitrobenzylammonium bromide (compound 15) of General Formula I by the Method Outlined in Scheme 2

A mixture of the free base of N-[(dimethylamino)ethyl]acridine-4-carboxamide (DACA) (37) [Atwell, Rewcastle, Baguley and Denny, J. Med. Chem. 30: 664-669, 1987] (1.13 g, 3.86 mmol) and 4-nitrobenzyl bromide (1.84 g, 8.50 mmol) in dry benzene (100 mL) was heated under reflux for 19 h and cooled. The resulting precipitate was filtered off and washed several times with dichloromethane to give 2-[N-(acridin-4-yl)carbonyl]aminoethyl-(dimethyl)-4-nitrobenzyl ammonium bromide (compound 15) (2.0 g, 100%), mp 170-172° C. (dec.). ¹ H NMR [(CD₃)₂ SO] d 11.63 (t, J=5.8 Hz, 1H, exchangeable with D₂ O, NH), 9.38 (s, 1 H, H-9), 8.77 (dd, J=7.1, 1.5 Hz, 1 H, H-3), 8.45 (dd, J=8.4, 1.5 Hz, 1 H, H-1), 8.42 (dd, J=8.8, 1.0 Hz, 1 H, H-5), 8.38 (br d, J=8.7 Hz, 2 H, phenyl H), 8.28 (dd, J=8.3, 1.0 Hz, 1 H, H-8), 7.90 (ddd, J=8.8, 6.6, 1.0 Hz, 1 H, H-6), 7.95 (br d, J=8.7 Hz, 2 H, phenyl H), 7.80 (dd, J=8.4, 7.1 Hz, 1 H, H-2), 7.74 (ddd, J=8.3, 6.6, 1.0 Hz, 1 H, H-7), 4.89 (s, 2 H, CH₂), 4.17 (q, collapsed to t after D₂ O, J=6.4 Hz, 2 H, NHCH₂), 3.74 (t, J=6.4 Hz, 2 H, NHCH₂ CH₂), 3.21 (s, 6 H, CH₃). Anal. Calculated for *CRL7459.

EXAMPLE 5b Preparation of 2-[N-(acridin-4-yl)carbonyl]aminoethyl-(dimethyl)-(5-nitro-2-thienyl)methylammonium chloride (compound 16) of General Formula I by the Method Outlined in Scheme 2

A mixture of the free base of DACA (37) (0.21 g, 0.70 mmol) and 2-chloromethyl-5-nitrothiophene [Newcombe P. J. and Norris R. K. Aust. J. Chem. 1979, 32, 2647-58 ](0.12 g, 0.67 mmol) in benzene (20 mL) was stirred at reflux temperature for 53 h. Cooling the mixture to room temperature gave a precipitate of 2-[N-(acridin-4-yl)carbonyl]aminoethjyl-(dimethyl)-(5-nitro-2-thienyl)methylammonium chloride (compound 16) (0.27 g, 86%), which was collected and washed with CH₂ Cl₂, mp 180-182° C. (dec.) ¹ H NMR [(CD₃)₂ SO] δ 11.64 (t, J=6.0 Hz, 1 H, exchangeable with D₂ O, NH), 9.38 (s, 1 H, H-9), 8.76 (dd, J=7.0, 1.4 Hz, 1 H, H-3), 8.46 (d, J=8.0 Hz, 1 H, H-5), 8.44(dd, J=8.0, 1.4 Hz, 1 H, H-1), 8.27 (br s, J=8.0 Hz, 1 H, H-8), 8.22 (d, J=4.2 Hz, thienyl H-4), 8.00 (td, J=8.0, 1.0 Hz, 1 H, H-6), 7.80 (dd, J=8.0, 7.0 Hz, 1 H, H-2), 7.74(t, J=8.0 Hz, 1 H, H-7), 7.63 (d, J=4.2 Hz thienyl H-3), 5.12 (s, 2 H, thienyl-CH₂), 4.16 (q, J=6.0 Hz, 2 H, collapsed to a t after D₂ O, NHCH₂), 3.77 (t, J=6.0 Hz, 2 H, NHCH₂ CH₂), 3.27 (s, 6 H, CH₃). Anal. Calculated for C₂₃ H₂₃ ClN₄ O₃ S: C, 58.7; H, 4.9; N, 11.9; Cl, 7.5. Found: C, 58.2; H, 5.3; N, 11.5; Cl, 7.6%.

EXAMPLE 5c Preparation of 2-[N-(9-amino-5-methylacridin-4-yl)carbonyl]aminoethyl-(dimethyl)-4-nitrobenzylammonium bromide (compound 17) of General Formula I by the Method Outlined in Scheme 2

Reaction of the free base of (N,N-dimethylaminoethyl)-9-amino-5-methylacridine-4-carboxamide (AMAC) (38) (for preparation see Rewcastle, Atwell, Chambers, Baguley and Denny, J. Med. Chem., 29, 472-477, 1986) with 4-nitrobenzyl bromide in dry benzene [using the procedure of Example 5a] gave 2-[N-(9-amino-5-methylacridin-4-yl)carbonyl]aminoethyl-(dimethyl)-4-nitrobenzylammonium bromide (compound 17) in 95% yield, mp 197-199° C. (dec.). ¹ H NMR [(CD₃)₂ SO)] δ 12.95(t, J=6.0 Hz, 1 H, exchangeable with D₂ O, CONH), 4.10 (br q, collapsing to a t after D₂ O, J=7.0 Hz, 2 H, CONHCH₂), 3.66 (t, J=7.0 Hz, 2 H, CONHCH₂ CH₂), 8.66 (d, J=7.5 Hz, 2 H, H-1,3), 8.37 (br d, J=8.8 Hz, 2 H, ArH), 8.33 (d, J=8.6 Hz, 1 H, H-8), 8.23 (br s, 2 H, exchangeable with D₂ O, NH₂), 7.93 (br s, J=8.8 Hz, 2 H, ArH), 7.69 (d, J=6.7 Hz, 1 H, H-6), 7.47 (t, J=7.5 Hz, 1 H, H-2), 7.32 (dd, J=8.6, 6.7 Hz, 1 H, H-7), 4.83 (s, 2 H, ArCH₂), 3.15 (s, 6 H, NCH₃), 2.74 (s, 3 H, ArCH₃). Anal. Calcd. for C₂₆ H₂₈ BrN₅ O₃.H₂ O: C, 56.1; H, 5.4; N, 12.6. Found: C, 56.6; H, 5.4, N, 12,4%.

EXAMPLE 5d Preparation of 2-[N-(9-amino-5-methylacridin-4-yl)carbonyl]aminoethyl-(dimethyl)-2-nitrobenzyl]ammonium chloride (compound 18) of General Formula I by the Method Outlined in Scheme 2

A mixture of AMAC (38) (0.15 g, 0.47 mmol) and 2-nitrobenzyl chloride (0.19 g, 1.12 mmol) in MeCN (10 mL) was stirred under reflux for 3 d. The mixture was then cooled to room temperature and the orange solid filtered off, washed with CH₂ Cl₂ and dried to give pure (98% by HPLC) 2-[N-(9-amino-5-methylacridin-4-y)carbonyl]aminoethyl-(dimethyl)-2-nitrobenzyl-ammonium chloride (compound 18) (0.22 g, 94%), mp 264-266° C. Repeated recrystallization from MeOH/Et₂ O or MeOH/EtOAc gave material of 99+% purity. ¹ H NMR [(CD₃)₂ SO] δ 12.94 (t, J=6.0 Hz, 1 H, exchangeable with D₂ O, CONH), 8.69-7.31 (m, 10 H, ArH), 8.25 (s, 2 H, exchangeable with D₂ O, NH₂), 5.05 (s, 2 H, benzylic CH₂), 4.07 (br q, J=6.0 Hz, 2 H, collapsed to a t after D₂ O, J=6.9 Hz, CONH CH₂), 3.74 (t, J=6.9 Hz, 2 H, CONHCH₂ CH₂), 3.12 (s, 6 H, NCH₃), 2.74 (s, 3 H, CH₃). Anal. Calculated for C₂₆ H₂₈ ClN₅ O₃ : C, 63.2; H, 5.7; N, 14.2; Cl, 7.2. Found: C, 63.3; H, 5.5; N, 14.4; Cl, 7.5%.

EXAMPLE 5e Preparation of 2-[N-(9-amino-5-methylacridin-4-yl)carbonyl]aminoethyl-(dimethyl)-5-nitro-2-thienylmethylammonium chloride (compound 19) of General Formula I by the Method Outlined in Scheme 2

Reaction of AMAC (38) (0.16 g, 0.50 mmol) and 2-chloromethyl-5-nitrothiophene [for preparation see Newcombe, P. J. and Norris, R. K. Aust. J Chem. 1979, 32, 2647-2658] (0.18 g, 1.00 mmol) under reflux for 16 h [as described for the preparation of SN 26208 above] gave 2-[N-(9-amino-5-methylacridin-4-yl)carbonyl]aminoethyl-(dimethyl)-5-nitro-2-thienylmethyl-ammonium chloride (compound 19) as a hydrochloride salt (0.21 g, 78%), mp 205° C. (dec). ¹ H NMR [(CD₃)₂ SO] δ 14.32 (s, 1 H, exchangeable with D₂ O), HCl), 10.38-10.34 (2s, 2 H, exchangeable with D₂ O, NH₂), 10.10 (br.t, J=5.5 Hz, 1 H, exchangeable with D₂ O, CONH), 9.02 (d, J=8.0 Hz, 1 H, H-3), 8.83 (d, J=8.0 Hz, 1 H, H-1), 8.61 (d, J=8.5 Hz, 1 H, H-8), 8.21 (d, J=4.2 Hz, 1 H, thienyl H-4), 7.98 (d, J=7.1 Hz, 1 H, H-6), 7.76 (t, J=8.0 Hz, 1 H, H-2), 7.62 (d, J=4.2 Hz, 1 H, thienyl H-3), 7.58 (dd, J=8.5, 7.1 Hz, 1 H, H-7), 5.08 (s, 2 H, thienyl CH₂), 3.98 (br q, J=5.5 Hz, collapsing to a t after D₂ O, 2 H, J=6.4 Hz, CONHCH₂), 3.73 (t, J=6.4 Hz, 2 H, CONHCH₂ CH₂), 3.23 (s, 6 H, NCH₃), 2.69 (s, 3 H, ArCH₃). Anal. Calculated for C₂₄ H₂₆ ClN₅ O₃ S.HCl: C, 53.7; H, 5.1; N, 13.1. Found: C, 53.5; H;, 5.8; N, 12.8%.

EXAMPLE 5f Preparation of 2-[N-(9-amino-5-methylacridin-4-yl)carbonyl]aminoethyl-(dimethyl)-2-[4-morpholino-5-nitro-4-thiazolylmethyl]ammonium chloride (compound 20) of General Formula I by the Method Outlined in Scheme 2

A solution of 2-(4-morpholino)-5-nitrothiazole (39) [for preparation see Lee, H. H.; Palmer, B. D.; Boyd, M. and Denny, W. A. J. Heterocycl. Chem. in press] (6.57 g, 30.6 mmol) and tert-butyl 2,2-dichloroacetate (8.50 g, 45.9 mmol) in DMF (50 mL) was added slowly to a stirred mixture of potassium tert-butoxide (12.0 g, 107 mmol) and dry DMF (50 mL) at -40° C. under N₂. The mixture was stirred for a further 1.5 h while the temperature allowed to rise to slowly to -10° C. It was then poured into excess 1% aqueous HCl, and extracted with EtOAc. Workup of the organic layer gave an orange solid which was triturated with MeOH/H₂ O (1:3), then filtered off and dried to give tert.-butyl 2-chloro-2-[2-(4-morpholino)-5-nitro-4-thiazolyl]acetate (40) (10.7 g, 95%), mp (EtOAc) 163-165° C. ¹ H NMR (CDCl₃) δ 6.15 (s, 1 H, CH), 3.9-3.5 (m, (8 H, morpholino H), 1.48 (s, 9 H, CH₃). Anal. Calculated for C₁₃ H₁₈ ClN₃ O₅ S: C, 42.9; H, 5.0; N, 11.6; Cl, 9.7. Found: C, 42.6; H, 5.2; N, 11.6; Cl, 10.0%.

A solution of the above acetate (40) (10.7 g, 29.3 mmol) in AcOH (300 mL) was heated under reflux for 1.5 h, then cooled, concentrated under reduced pressure to ca. 50 mL, and poured into ice-water. Extraction with EtOAc and chromatography of the crude product on silica gel, eluting with EtOAc/petroleum ether (1:4), gave 4-chloromethyl-2-(4-morpholino)-5-nitrothiazole (41) (2.99 g, 39%), mp (EtOAc/petroleum ether) 119-121° C. ¹ H NMR (CDCl₃) δ 4.87 (s, 2 H, CH₂ Cl). 4.0-3.5 (m, 8 H, morpholino H). Anal. Calculated for C₈ H₁₀ ClN₃ O₃ S: C, 36.4; H, 3.8; N, 15.9; Cl, 13.4. Found: C, 36.7; H, 3.7; N, 15.8; Cl, 13.6%.

A mixture of the above chloride (41) (0.40 g, 1.50 mmol) and AMAC (31) (0.16 g, 0.50 mmol) was heated under reflux for 3 days using the procedure described above gave a crude product which was chromatographed on a short column of silica gel. Elution with CHCl₃ /MeOH/Et₃ N (5:1:2) gave 2-[N-(9-amino-5-methylacridin-4-yl)carbonyl]aminoethyl-(dimethyl)-(2-[4-morpholino-5-nitro-4-thiazolyhnethyl]ammonium hydroxide (compound 20) (0.27 g, 95%), mp (MeOH/Et₂ O) 133° C. (dec.). ¹ H NMR [(CD₃)₂ SO] δ 12.97 (t, J=5.8 Hz, 1 H, exchangeable with D₂ O, CONH), 7.3-8.6 (m 6 H, ArH), 8.19 (s, 2 H, exchangeable with D₂ O, NH₂), 6.58 (s, 1 H, exchangeable with D₂ O, OH), 5.01 (s, 2 H, thiazolyl CH₂), 3.50-4.20 (m, 12 H, CH₂ CH₂ and morpholino H), 3.45 (s, 6 H, NCH₃), 2.63 (s, 3 H, ArCH₃). Anal. Calculated for C₂₇ H₃₃ N₇ O₅ S.0.5H₂ O: C, 56.2; H, 5.9; N, 17.0. Found: C, 56.3; H, 6.6; N, 17.0%. Treatment of a solution of the above hydroxide in MeOH with excess concentrated HCl gave the hydrochloride salt (compound 16), mp 244-246° C. (dec.).

EXAMPLE 5g Preparation of 2-(N-[9-amino-5-methylacridin-5-yl]carbonyl)aminoethyl-(dimethyl)[1-methyl-5-nitro-2-pyrrolyl]methylammonium chloride (compound 21) of General Formula I by the Method Outlined in Scheme 2

Solid NaBH₄ (0.19 g, 5.03 mmol) was added portionwise to a stirred solution of 1-methyl-5-nitro-2-pyrrolealdehyde (42) [for preparation see Fournari, P. Bull. Soc. Chim. Fr., 88, 488-491, 1963] (0.78 g, 5.07 mmol) in MeOH (40 mL) at room temperature under N₂. After addition was complete, the reaction mixture was stirred for a further 20 min, then water (40 mL) was added and the mixture was saturated with solid K₂ CO₃. Extraction with EtOAc gave 2-hydroxymethyl-1-methyl-5-nitropyrrole (43) (0.77 g, 97%), mp (EtOAc/petroleum ether) 76-77° C. ¹ H NMR (CDCl₃) δ 7.16 (d, J=4.3 Hz, 1 H, H-4), 6.17 (d, J=4.3 Hz, 1 H, H-3), 4.68 (s, 2 H, CH₂), 4.02 (s, 3 H, CH₃). Anal. Calculated for C₆ H₈ N₂ O₃ : C, 45.1; H, 5.2; N, 17.9. Found: C, 46.1; H, 5.1; N, 17.6%.

A stirred solution of the above alcohol (43) (0.13 g, 0.83 mmol) in dry CH₂ Cl₂ (5 mL) at 0° C. was treated with methanesulfonyl chloride (0.36 mL. 1.25 mmol), followed by Et₃ N (0.50 mL). After stirring at 0° C. for 15 min, the mixture was evaporated to dryness under reduced pressure at room temperature, and the resulting brown solid was partitioned between water and EtOAc. Workup of the organic layer gave a crude product which was was chromatographed on silica gel. Elution with CH₂ Cl₂ /petroleum ether (1:1) gave 1-methyl-2-chloromethyl-5-nitropyrrole (44) (0.13 g, 88%), mp (EtOAc/petroleum ether) 82.5-83.5° C. ¹ H NMR (CDCl₃) δ 7.16 (d, J=4.4 Hz, 1 H, H-4), 6.26 (d, J=4.4 Hz, 1 H, H-3), 4.60 (s, 2 H, CH₂ Cl), 4.02 (s, 3 H, CH₃). Anal. Calculated for C₆ H₇ ClN₂ O₂ : C, 41.3; H, 4.0; N, 16.0. Found: C, 41.4; H, 4.0; N, 15.9%.

Reaction of the above chloride (44) (0.18 g, 1.00 mmol) and AMAC (38) (0.16 g, 0.50 mmol) as described in Example 5a above gave 2-(N-[9-amino-5-methylacridin-5-yl]carbonyl)aminoethyl(dimethyl)[1-methyl-5-nitro-2-pyrrolyl]methylammonium chloride (compound 21) in quantitative yield, mp (MeOH/EtOAc) 188-190° C. (dec). ¹ H NMR [(CD₃)₂ SO]δ 12.98 (t, J=6.0 Hz, 1 H, exchangeable with D₂ O, CONH), 8.69 (d, J=8.5 Hz, 1 H, H-3), 8.65 (d, J=7.2 Hz, 1 H, H-1), 8.35 (d, J=8.6 Hz, 1 H, H-8), 8.28 (s, 2 H, exchangeable with D₂ O, NH₂), 7.69 (d, J=6.8 Hz, 1 H, H-6), 7.46 (dd, J=8.5, 7.2 Hz, 1 H, H-2), 7.36 (d, J=4.5 Hz, 1 H, pyrrolyl H-4), 7.32 (dd, J=8.6, 6.8 Hz, 1 H, H-7), 6.74 (d, J=4.5 Hz, 1 H, pyrrolyl H-3), 4.89 (s, 2 H, pyrrolyl CH₂), 4.08 (q, J=6.0 Hz, collapsed to a t after D₂ O, J=6.8 Hz, 2 H, CONHCH₂), 4.01 (s, 3 H, pyrrolyl CH₃), 3.72 (t, J=6.8 Hz, 2 H, CONHCH₂), 3.16 (s, 6 H, NCH₃), 2.75 (s, 3 H, ArCH₃). Anal. Calculated for C₂₅ H₂₉ ClN₆ O₃.0.5H₂ O: C, 59.3; H, 6.0; N, 16.6. Found: C, 59.4, H, 6.7; N, 16.6%.

EXAMPLE 5h Preparation of 2-(N-[9-amino-5-methylacridin-4-yl]carbonyl)aminoethyl-(dimethyl)-(1-methyl-4-nitro-5-imidazolyl)methylammonium chloride (compound 22) of General Formula I by the Method Outlined in Scheme 2

Reaction of 1-methyl-4-nitro-5-imidazolyl)methyl chloride [for preparation see M. Makosza and M. Bialecki, Synlett., 181-182, 1991] (0.35 g, 1.00 mmol) and AMAC (38) (0.16 g, 0.50 mmol) under reflux for 3 days as described as in Example 5a above gave 2-(N-[9-amino-5-methylacridin-4-yl]carbonyl)aminoethyl-(dimethyl)-(1-methyl-4-nitro-5-imidazolyl)methylammonium chloride (compound 22) (0.20 g, 80%), mp (MeOH/EtOAc) 245° C. (dec.). ¹ H NMR [(CD₃)₂ SO] δ 13.0 (t, J=6.0 Hz, 1 H, exchangeable with D₂ O, CONH₂), 8.66 (m, 2 H, H-1, H-3), 8.33 (d, J=8.6 Hz, 1 H, H-8), 8.24 (s, 2 H, exchangeable with D₂ O, NH₂), 8.12 (s, 1 H, imidazolyl H-2), 7.70 (d, J=6.7 Hz, 1 H, H-6), 7.46 (dd, J=8.3, 7.4 Hz, 1 H, H-2), 7.32 (dd, J=8.6, 6.7 Hz, 1 H, H-7), 4.09 (q, J=6.0 Hz, collapsed to a t, J=6.5 Hz, 2 H, COHNCH₂), 3.89 (t, J=6.5 Hz, 2 H, CONHCH₂ CH₂), 3.87 (s, 3 H, imidazolyl CH₃), 3.20 (s, 6 H, NCH₃), 2.76 (s, 3 H, ArCH₃). Anal. Calculated for C₂₄ H₂₈ ClN₇ O₃.H₂ O: C, 55.9; H, 5.9; N, 19.0. Found: C, 56.4; H, 6.3; N, 19.1%.

EXAMPLE 5i Preparation of 2-(N-[9-amino-5-methylacridin-4-yl]carbonyl)aminoethyl-(dimethyl)-(3-nitro-2-thienyl)methylamonium chloride (compound 23) of General Formula I by the Method Outlined in Scheme 2

A mixture of AMAC (38) (0.16 g, 0.50 mmol) and 2-bromomethyl-3-nitrothiophene (0.17 g, 0.75 mmol) in meCN (10 mL) was heated under reflux for 21 h, giving an orange precipitate. The mixture was cooled to room temperature and the precipitate was collected and washed with EtOAc, then dissolved in MeOH/water (1:) and treated with a large excess of Biorad AG 1-X4 ion exchange resin (Cl⁻ form) for 2 h. Filtration and evaporation of the filtrate gave 2-(N-[9-amino-5-methylacridin-4-yl]carbonyl)aminoethyl-(dimethyl)-(3-nitro-2-thienyl)methylammonium chloride (compound 23) (0.25 g, 100%), mp (MeOH/EtOAc) 190° C. (dec.) ¹ H NNR [(CD₃)₂ SO] δ 14.31 (s, 1H, exchangeable with D₂ O), Hcl), 10.50 (s, 1H, exchangeable with D₂ O), NH₂), 10.44 (s, 1H, exchangeable with D₂ O, NH₂), 10.21 (t, J=5.4 Hz, collapsing to a t after D₂ O, 1H, CONH), 9.08 (t, J=8.4 Hz, 1H, H-3), 8.86 (d, J=7.1 Hz 1 H, H-1), 8.66 (d, J=8.5 Hz, 1H, H-8) 8.06 (d, J=5.7 Hz, 1H, thienyl H-5), 7.97 (d, J=7.0 Hz, 1H, H-6), 7.86 (d,J=6.7 Hz, 1H, thienyl H-4), 7.74 (dd, J=8.4, 7.1 Hz, 1H, H-2), 7.56 (dd, J=8.5, 7.0 Hz, 1H, H-7), 5.33 (s, 2H, CH₂), 3.97 (br q, J=5.4 Hz, collapsing to a t after D₂ O), 2H, CONHCH₂), 3.87 (t, J=5.5 Hz, 2H, CONHCH₂ CH₂), 3.27 (s, 6H, N(CH₃)₂), 2.69 (s, 3 H, ArCH₃).

EXAMPLE 6a Preparation of 1,4-bis[((2-(4-nitrobenzyl)dimethylammonium)-ethyl)amino]-9,10-anthracenedione dichloride (compound 24) of General Formula I by the Method Outlined in Scheme 3

A mixture of 1,4-bis(2-dimethylaminoethylamino)-9,10-anthracenedione (45) [for preparation see Zee-Cheng and Cheng, J. Med. Chem. 1978, 21, 291-294] (0.19 g, 0.50 mmol) and 4-nitrobenzyl chloride (86 mg, 0.50 mmol) in acetonitrile (50 mL) was stirred under reflux for 30 h, then cooled and evaporated to dryness under reduced pressure. The resulting deep blue solid was chromatographed on silica gel, and elution with acetonitrile/water/AcOH (10:1:1). The appropriate fractions were pooled and evaporated, and the residue was extracted with EtOAc/MeOH (10:1) and filtered. On standing the filtrate deposited 1,4-bis[((2-(4-nitrobenzyl)dimethylammonium)ethyl)amino]-9,10-anthracenedione dichloride (compound 24) (132 mg, 36%), mp 245° C. (dec.). ¹ H NMR [(CD₃)₂ SO] δ 10.66 (t, J=6.0 Hz, 2 H, exchangeable with D₂ O, NH), 8.39 (d, J=8.8 Hz, 2 H, ArH), 8.24 (m, 2 H, H-5,8), 7.91 (d, J=8.8 Hz, 2 H, ArH), 7.85 (m, 2 H, H-6,7), 7.62 (s, 2 H, H-2,3), 4.85 (s, 2 H, CH₂), 4.10 (q, J=6.0 Hz, 4 H, collapsed to at after D₂ O, NHCH₂), 3.71 (t, J=6.0 Hz, 4 H, NHCH₂ CH₂), 3,10 (s, 12 H, NCH₃). Anal. Calculated for C₃₆ H₄₀ Cl₂ N₆ O₆.H₂ O: C, 58.3; H, 5.7; N, 11.3; Cl, 9.6. Found: C, 58.8; H, 5.9; N, 11.2; Cl, 9.8%.

EXAMPLE 6b Preparation of 1-(2-(4-nitrobenzyl)dimethylaminoethylammonium)-4-(2-dimethylamino)ethylammino-9,10-anthracenedione acetate (compound 25) of General Formulla I by the Method Outlined in Scheme 3

Later fractions eluted from the column in Example 6a were also pooled and evaporated, and the residue was extracted with EtOAc/CH₂ Cl₂ (2:1) and filtered. On cooling the filtrate deposited 1-(2-(4-nitrobenzyl)dimethylaminoethylammonium)-4-(2-dimethylaminoethylamino)-9,10-anthracenedione acetate (compound 25) (117 mg, 38%), mp 124-125° C. ¹ H NMR [(CD₃)₂ SO] δ 10.65 (m, 3 H, exchangeable with D₂ O, NH and COOH), 8.39 (d, J=8.7 Hz, 2 H, ArH), 8.25 (m, 2 H, H-5,8), 7.92 (d, J=8.7 Hz, 2 H, ArH), 7.85 (m, 2 H, H-6,7), 7.69 (d, J=9.8 Hz, 1 H,H-3), 7.62 (d, J=9.8 Hz, 1 H, H-2), 4.12 (q, J=6.5 Hz, 2 H, collapsed to a t after D₂ O, NHCH₂), 3.94 (q, J=6.5 Hz, 2 H, collapsed to a t after D₂ O, NHCH₂), 3.71 (t, J=6.5 Hz, 2 H, CH₂ N), 3.15 (s, 6 H, NCH₃), 2.84 (s, 6 H, NCH₃), 2.49 (s, 3 H, CH₃ CO). Anal. Calculated for C₃₁ H₃₇ N₅ O₆.0.5H₂ O: C, 63.7; H, 6.6; N, 12.0. Found: C, 63.9; H, 7.1; N, 12.0%.

EXAMPLE 6c Preparation of 1,4-bis[(2-(4-nitrobenzyl)dimethyl-ammonium)ethylamino]-5,8-dihydroxy-9,10-anthracenedione dichloride (compound 26) of General Formula I by the Method Outlined in Scheme 3

Leuco-1,4,5,8-tetrahydroxyanthraquinone was prepared from conumercially-available 1,5-diamino-4,8-dihydroxyanthraquinone by the published method [Chang, P. and Cheng, C. C. Synth. Comm., 25, 1893-1900, 1995], and this was converted to 1,4-bis[(2-dimethylamino)-ethylamino]-5,8-dihydroxy-9,10-anthracenedione (46) by the published method [see Murdock, K. C., Wallace, R. E., Durr, F. E., Childs, R. G., Citarella, R. V., Fabio, F. B. and Angier, R. B. J. Med. Chem., 22, 1024-1030, 1979]. A mixture of (46) (0.824 g, 2.00 mmol) and 4-nitrobenzyl chloride (3.44 g, 10.0 mmol) in MeCN (280 mL) were stirred at reflux temperature for 7 d. The solution was then evaporated to dryness under reduced pressure and the residue was purified by chromatography on silica gel, eluting with MeCN/water/AcOH (10:1:1). The appropriate fractions were pooled and evaporated to give a residue which was extracted with EtOAc/MeOH (10:1) and filtered. On cooling the filtrate deposited 1,4-bis[(2-(4-nitrobenzyl)dimethyl-ammonium)ethylamino]-5,8-dihydroxy-9,10-anthracenedione dichloride (compound 26), (0.34 g, 23%), mp (EtOAc/MeOH) 227-229° C. ¹ H NMR [(CD₃)₂ SO] δ 13.44 (s, 2 H, exchangeable with D₂ O, OH), 10.45 (br s, 2 H, exchangeable with D₂ O, NH), 8.39 (d, J=8.6 Hz, 4 H, ArH), 7.92 (d, J=8.6 Hz, 4 H, ArH), 7.70 (s, 2 H, H-6,7), 7.25 (s, 2 H, H-2,3), 4.86 (s, 4 H, CH₂ Ar), 4.15 (br q, 4 H, collapsed to a t after D₂ O, J=6.0 Hz, NHCH₂), 3.73 (t, J=6.0 Hz, 4 H, CH₂ N), 3.15 (s, 12 H, CH₃. Anal. Calculated for C₃₆ H₄₈ Cl₂ N₆ O₈.H₂ O: C, 55.9; H, 5.5; N, 10.9; Cl, 9.2. Found: C, 55.9; H, 5.4; N, 10.5; Cl, 9.2%.

EXAMPLE 6d Preparation of 1-[(2-(4-nitrobenzyl)dimethylammonium)ethylamino]-4-[(2-dimethylamino)ethylamino]-5,8-dihydroxy-9,10-anthracenedione chloride (compound 27) of General Formula I by the Method Outlined in Scheme 3

Continued elution of the column in Example 6c gave 1-[(2-(4-nittobenzyl)dimethylammonium)-ethylamino]-4-[(2-dimethylamino)ethylamino]-5,8-dihydroxy-9,10-anthracenedione chloride (compound 27) (0.73 g, 62%), mp (EtOAc/MeOH) 136-138° C. ¹ H NMR (CD₃ OD) δ 8.40 (br s, 2 H, ArH), 7.89 (br s, 2 H, ArH), 7.43 (s, 2 H, H-6,7), 7.12 (s, 2 H, H-2,3), 4.13 (br s, 2 H, NHCH₂), 3.77 (br s, 2 H, NHCH₂), 3.62 (br s, 2 H, CH₂ N), 3.25 (s, 6 H, CH₃), 2.78 (br s, 2 H, CH₂ N), 2.43 (s, 6 H, CH₃). Anal. Calculated for C29H₃₅ Cl₂ N₅ O₆ : C, 56.1; H, 5.7; N, 11.3; Cl, 11.4. Found: C, 55.6; H, 6.1; N, 11.0; Cl, 11.2%.

EXAMPLE 7a Preparation of bis(3-methyl-2,4-pentanedionato)(N-[3-[(2-aminoethyl)-amino]propyl]acridine-4-carboxamide)cobalt(III) perchlorate, (compound 28) of General Formula I by the Method Outlined in Scheme 4

N-[3-[(2-Aminoethyl)amino]propyl]acridine-4-carboxamide trihydrochloride (47) [for preparation see Lee H H, Palmer B D, Baguley B C, Chin M, McFadyen W D, Wickham, G, Thorsbourne-Palmer D, Wakelin L P G and Denny V A. J. Med. Chem. 35, 2983-2987, 1992] (0.200 g, 0.445 mmol) was suspended in a solution containing Co(Mecac)₃ (0.177 g, 0.445 mmol) dissolved in MeOH (5 ml). A 1.0 M solution of KOH in MeOH (1.33 ml, 3 eq.) was added followed immediately by charcoal (0.100 g). The mixture was stirred at ambient temperature for 2 h, then filtered through Celite and the collected charcoal washed with a portion of MeOH. The combined filtrate plus washings were combined with aqueous 3 M NaClO₄ and extracted with CH₂ Cl₂ (3×). The purple-red organic phase was evaporated to dryness and chromatographed on silica gel. Elution with acetone/CH₂ Cl₂ (progressively increasing concentration of acetone up to 50%) eluted two nearly resolved reddish purple bands. In each case the solvent was removed under reduced pressure to give a purple residue (1st band=36 mg, 2nd band=140 mg). These compounds are the two diastereoisomers (enantiomeric pairs: Δ(S), Λ(R) and Δ(R), Λ(S)) of bis(3-methyl-2,4-pentanedionato)(N-[3-[(2-aminoethyl)amino]propyl]acridine-4-carboxamide)cobalt(III) perchlorate (28) (176 mg, 56.1%) ¹ H NMR (CDCl₃) δ 11.91 (br t, 1H, NHCO, J=6.0 Hz), 8.93 (s, 1H, H-9), 8.71 (d-d, 1H, H-5, J=7.0, 1.2 Hz), 8.22 (d, 1H, H-1), 8.19 (d, 1H, H-8), 8.06 (d, 1H, H-3, J=8.4 Hz), 7.89 (t-d, 1H, H-6, J=7.0, 1.1 Hz), 7.66 (t, 1H, H-7, J=7.7 Hz), 7.63 (t, 1H, H-2, J=7.6 Hz), 4.95 (br, 1H, NH), 4.07 (br q, 1H, NH, J=7.3 Hz), 3.91, 3.60 (m, 1H, CH₂ NHCO), 3.39 (br d, 1H, NH, J=8.2 Hz), 3.03 (m, 2H, CH₂ NHR), 2.97, 2.80 (m, 1H, CH₂ NHR), 2.87 (m, 2H, CH₂ NH₂), 2.31, 2.19, 2.10, 1.82 (s, 3H, CH₃ CO), 2.25, 2.07 (m, 1H, CH₂ CH₂ CH₂), 1.67, 1.63 (s, 3H, CH₃ --C). ¹³ C NMR (CDCl₃) δ 188.79, 2× 188.01, 187.66 (CO), 166.92 (CONH), 147.61, 145.96 (C-12,13), 138.16 (C-9), 135.08, 132.96 (C-1,8), 131.90 (C-5), 128.91, 128.17 (C-3,6), 127.32, 126.04 (C-11,14), 126.70, 125.08 (C-2,7); 101.82, 101.78 (C--CH₃), 51.67, (CH₂ NHCO), 43.95, 43.09 (CH₂ NHR), 35.80 (CH₂ NH₂), 26.72, 26.55, 26.22, 25.83 (CH₃ CO), 26.51 (CH₂ CH₂ CH₂), 15.15, 15.00 (CH₃ -C). HRMS (FAB⁺) Calc. for C₃₁ H₄₀ N₄ O₅ Co; 607.2331. Found 317.607.2354.

EXAMPLE 8 Preparation of Cyclopropylindole Precursors 32

A solution of 4-chloro-3-nitrobenzoic acid (10.03 g, 50 mmol), SOCl₂ (4.4 mL, 60 mmol) and DMF (4 drops) in 1,2-dichloroethane (150 mL) was stirred under reflux for 14 h, cooled and evaporated. The resulting crude acid chloride was dissolved in THF (100 mL), cooled to 0° C., and a solution of potassium t-butoxide (5.57 g, 50 mmol) in THF (150 mL) was added dropwise over 30 min under nitrogen. The mixture was stirred a further 15 min at 0° C., diluted with aqueous NaHCO₃ and extracted with EtOAc (×2), and the extracts were dried (Na₂ SO₄) and evaporated. Flash chromatography of the residue on silica gel (petroleum ether/EtOAc; 30:1) gave t-butyl 4-chloro-3-nitrobenzoate as a white crystalline solid (11.45 g, 89%), mp (petroleum ether) 70-71° C. ¹ H NMR (CDCl₃) d 8.42 (d, J=2.0 Hz, 1 H, H-2), 8.11 (dd, J=8.4, 2.0 Hz, 1 H, H-6), 7.61 (d, J=8.4 Hz, 1 H, H-5), 1.61 (s, 9 H, t-Bu). Anal. Calculated for C₁₁ H₁₂ ClNO₄ : 51.3; H, 4.7; N, 5.4; Cl, 13.8. Found: C, 51.6; H, 4.8; N, 5.4; Cl, 14.0%.

Sodium hydride (13.5 g of a 60% dispersion in oil, 0.34 mol) was washed with petroleum ether (×3) under nitrogen and suspended in dry THF (400 mL). A solution of dimethyl malonate (40.4 mL, 0.35 mol) in THF (50 mL) was added dropwise over 45 min with water-bath cooling, keeping the internal temperature below 30° C., and the resulting gel was broken up with more dry THF (300 mL). The above t-Butyl 4-chloro-3-nitrobenzoate (21.7 g, 84 mmol) was added and the mixture was stirred at reflux under nitrogen for 15 h. The red-brown solution was cooled, poured into water, and aqueous HCl (2 N, ca. 60 mL) added slowly until the red nitronate color was dispersed. The THF was evaporated and the aqueous phase extracted with CH₂ Cl₂ (×3), the extracts were dried (Na₂ SO₄) and evaporated. Formic acid (100 mL) was added to the residue and the mixture was stirred at 50° C. for 4 h (when tlc analysis showed no remaining t-butyl ester). The formic acid was evaporated and the residue was taken up in EtOAc and washed with water (×3). The organic layer was extracted with aqueous NaHCO₃ (×2), and the aqueous phase was acidified (conc. HCl), and extracted with CH₂ Cl₂ (×2). The organic layer was dried (Na₂ SO₄), evaporated, and the resulting cream solid recrystallized from benzene (ca. 250 mL) to give dimethyl (4-carboxy-2-nitrophenyl)malonate as cream prisms (21.8 g, 87%), mp 147-149° C. ¹ H NMR ((CD₃)₂ SO) d 13.77 (br s, 1 H, CO₂ H), 8.52 (d, J=1.7Hz, 1 H, H-3), 8.28 (dd, J=8.1, 1.7 Hz, 1 H, H-5), 7.70 (d, J=8.1 Hz, 1 H, H-6), 5.62 (s, 1 H, ArCH), 3.71 (s, 6 H, CO₂ Me); ¹³ C NMR ((CD₃)₂ SO) d 166.9, 165.1, 148.2, 134.0, 133.1, 132.3, 132.1, 125.5 (CO₂ Me, C-1,2,3,4,5,6), 54.3 (ArCH), 52.9 (OMe). Anal. Calculated for C₁₂ H₁₁ NO₈ : C, 48.5; H, 3.7; N, 4.7. Found: C, 48.7; H, 3.5; N, 4.7%.

A solution of the above malonate (3.44 g, 11.6 mmol), SOCl₂ (1.0 mL, 13.9 mmol) and DMF (4 drops) in 1,2-dichloroethane (60 mL) was stirred under reflux for 1 h, cooled and evaporated. The residue was dissolved in Me₂ CO (30 mL) and added dropwise over 10 min to a vigorously stirred solution of sodium azide (2.26 g, 35 mmol) in water (30 mL) and M acetone (100 mL) at 0° C. After a further 30 min at 0° C., EtOAc (100 mL) was added, most of the Me₂ CO was evaporated, and the EtOAc layer was washed with water, dried (Na₂ SO₄), and evaporated. The residue was dissolved in dry toluene (35 mL) and stirred at reflux for 40 min. Benzyl alcohol (2.2 mL, 21 mmol) was added to the cooled solution and the mixture stirred at 20° C. for 2 h [until a sample spotted on a tlc plate no longer showed the formation of yellow dimethyl (4-amino-2-nitrophenyl)malonate]. The mixture was then evaporated and the residue was distilled in a Kugelrohr (1 mm Hg, 90° C.) to remove excess benzyl alcohol. Flash chromatography on silca gel, eluting with petroleum ether/EtOAc (3:1) gave dimethyl [4-(benzyloxycarbonyl)amino-2-nitrophenyl]malonate as a yellow oil (3.77 g, 81%). ¹ H NMR (CDCl₃) 8.16 (d, J=2.3 Hz, 1 H, H-3), 7.59 (dd, J=8.5, 2.3 Hz, 1 H, H-5), 7.42-7.33 (m, 6 H, H-6 and Ph), 7.11 (s, 1 H, NH), 5.25 (s, 1 H, ArCH), 5.22 (s, 2 H, OCH₂ Ph), 3.78 (s, 6 H, CO₂ Me); ¹³ C NMR (CDCl₃) d 167.9, (CO₂ Me), 152.8 (NCO₂), 149.0, 139.1, 135.4, 131.9, 128.7, 128.6, 128.4, 122.7, 121.9, 114.6 (aromatic C), 67.6 (OCH₂ Ph), 53.5 (ArCH), 53.2 (OMe); MS (DEI) m/z 402 (2%, M⁺), 91 (100%, (C₇ H₇); HRMS calcd. for C₁₉ H₁₈ N₂ O₈ 402.10631, found 402.10594.

A solution of the above 2-nitrophenylmalonate (3.12 g, 7.75 mmol) in THF (80 mL) was added dropwise over 30 min to a solution of diisobutylaluminium hydride (93 mL of a 1M solution in hexanes, 93 mmol) in THF (100 mL) under nitrogen, with cooling in an ice-salt bath (maintaining the internal temperature at -7 to 0° C.). The mixture was allowed to warm to 20° C. over 1 h, then poured into ice-cold aqqueous HCl (3 N, 260 mL). The THF was evaporated, the aqueous residue was extracted with EtOAc (×3), and the extracts dried (Na₂ SO₄) and evaporated. Dry column chromatography on silica gel, eluting with EtOAc/petroleum ether (1:3 then 1:1 then 2:1) gave recovered dimethyl [4-(benzyloxycarbonyl)amino-2-nitrophenyl]malonate (0.42 g, 13%) and 2-[4-(benzyloxycarbonyl)amino-2-nitrophenyl]propane-1,3-diol as a light brown foam (1.35 g, 50%). A sample of the latter was crystallized from CHCl₃, giving pale yellow flakes, mp 119-121° C. ¹ H NMR ((CD₃)₂ SO) d 10.15 (s, 1 H, NH), 7.97 (d, J=2.2 Hz, 1 H, H-3), 7.60 (dd, J=8.6, 2.2 Hz, 1 H, H-5), 7.49 (d, J=8.6 Hz, 1 H, H-6), 7.45-7.33 (m, 5 H, Ph), 5.18 (s, 2 H, OCH₂ Ph), 4.67 (t, J=5.3 Hz, 2 H, OH), 3.73-3.66 (m, 2 H, CHHOH), 3.63-3.56 (m, 2 H, CHHOH), 3.23 (p, J 6.4 Hz, 1 H, ArCH); ¹³ C NMR ((CD₃)₂ SO) d 153.3 (NCO₂), 150.9, 137.8, 136.2, 129.0 (C-1,2,4 and i C of Ph), 129.9, 121.7, 112.3 C-3,5,6), 128.4, 128.11, 128.09, (o, m, p C of Ph), 66.1 (OCH₂ Ph), 61.8 (CH₂ OH), 44.1 (ArCH). Anal. Calculated for C₁₇ H₁₈ N₂ O₆ : C, 59.0; H, 5.2; N, 8.1. Found: (C, 58.9; H, 5.4; N, 8.3%.

A solution of the above nitrodiol (1.02 g, 2.9 mmol) in EtOH (80 mL) with PtO₂ (0.12 g) was hydrogenated at 50 psi and 20° C. for 50 min, filtered through Celite, and evaporated. Dry column chromatography on silica gel, eluting, with EtOAc/MeOH (20:1 then 10:1) gave 2-[2-amino-4-(benzyloxycarbonyl)aminophenyl]propane-1,3-diol as a very pale yellow oil (0.88 g, 94%). ¹ H NMR ((CD₃)₂ SO) d 9.36 (s, 1 H, NH), 7.43-7.30 (m, 5 H, Ph), 6.82 (d, J=2 Hz, 1 H, H-3), 6.81 (d, J=8.3 Hz, 1 H, H-6), 6.58 (dd, J=8.3, 2.1 Hz, 1 H, H-5), 5.12 (s, 2 H, OCH₂ Ph), 4.82 (s, 2 H, NH₂ or OH), 4.50 (s, 2 H NH₂ or OH), 3.69-3.62 (m, 2 H, CHHOH), 3.54-3.46 (m, 2 H, CHHOH), 2.83 (p, J=6.2 Hz, 1 H, ArCH); ¹³ C NMR ((CD₃)₂ SO) d 153.2 (NCO₂), 146.8, 137.2, 136.8, 120.4 (C-1,2,4 and i C of Ph), 128.3, 127.92, 127.86 (o, m, p C of Ph), 127.0, 107.2, 105.2 (C-3,5,6), 65.3 (OCH₂ Ph), 62.3 (CH₂ OH), 43.2 (ArCH); MS (DEI) m/z 316 (30%, M⁺), 285 (30%, M--CH₂ OH), 91 (100%, C₇ H₇); HRMS calcd. for C₁₇ H₂₀ N₂ O₄ 316.14231, found 316.14182.

A solution of the above aminodiol (0.70 g, 2.21 mmol), di-t-butyldicarbonate (0.53 g, 2.4 mmol) and Na₂ CO₃ (0.26 g, 2.4 mmol) in THF (120 mL) and water (60 mL) was stirred at 20° C. More di-t-butyldicarbonate (2×0.53 g) was; added after 5 and 8 days, with sufficient THF and water to maintain a single phase. After 14 days the THF was evaporated, the aqueous layer extracted with EtOAc (×2), and the organic extracts dried (Na₂ SO₄) and evaporated. Dry column chromatography on silica gel, eluting with EtOAc/petroleum ether (2:1 then 4:1) gave 2-[4-(benzyloxycarbonyl)amino-2-(t-butyloxycarbonyl)aminophenyl]propane-1,3-diol as a white foam (0.78 g, 85%). ¹ H NMR [(CD₃)₂ SO] d 9.67 (s, 1 H, NH), 8.62 (s, 1 H, NH), 7.60 (s, 1 H, H-3), 7.44-7.31 (m, 5 H, Ph), 7.19 (dd, J=8.5, 1.7 Hz, 1 H, H-5), 7.08 (d, J=8.5 Hz, 1 H, H-6), 5.14 (s, 2 H, OCH₂ Ph), 4.84 (t, J=4.7 Hz, 2 H, OH), 3.78-3.70 (m, 2 H, CHHOH), 3.54-3.45 (m, 2 H, CHHOH), 2.98 (p, J=6.3 Hz, 1 H, ArCH), 1.45 (s, 9 H, t-Bu). ¹³ C NMR d 153.3 (resolves into two peaks on D₂ O exchange, 2×NCO₂), 137.1, 137.0, 136.7, 129.4 (C-1,2,4 and i C of Ph), 128.4, 127.91, 127.87 (o, m, p C of Ph), 127.4, 114.6, 114.4 (C-3,5,6), 78.8 (OCMe₃), 65.5 (OCH₂ Ph), 62.8 (CH₂ OH), 43.9 (ArCH), 28.1 (C(CH₃)₃); MS (DEI) m/z 416 (2%, M⁺), 91 (100%, C₇ H₇); HRMS calcd. for C₂₂ H₂₈ N₂ O₆ 416.19474, found 416.19544.

Diethylazodicarboxylate (0.47 mL, 3.0 mmol) was added dropwise over 5 min to a solution of the above t-butyloxycarbonyl diol (0.74 g, 1.78 mmol) and triphenylphosphine (0.84 g, 3.2 mmol) in THF (60 mL) under nitrogen and the mixture stirred at 20° C. After 10 min the mixture was diluted with EtOAc, washed with aqqueous NaCl, and the organic phase dried (Na₂ SO₄) and evaporated. Dry column chromatography on silica gel, eluting with EtOAc/petroleum ether (1:2) gave an overlapping band of reduced diethylazodicarboxylate and 6-[(benzyloxycarbonyl)amino]-1-(t-butyloxycarbonyl)-3-(hydroxymethyl)indoline. A small fraction of the product was obtained in a pure state as a very pale yellow oil. ¹ H NMR ((CD₃)₂ SO) d 9.68 (s, 1 H, NH), 7.97 (br s, 1 H, H-7), 7.44-7.31 (m, 5 H, Ph), 7.11 (d, J=8.1 Hz, 1 H, H-4), 6.98 (br d, J=8 Hz, 1 H, H-5), 5.13 (s, 2 H, OCH₂ Ph), 4.90 (t, J=5.0 Hz, 1 H, OH), 3.94 (apparent t, J=10.3 Hz, 1 H, NCHH), 3.75 (dd, J=11.3, 5.1 Hz, 1 H, NCHH), 3.61-3.54 (m, collapses to dd, J=10.2, 4.7 Hz in D₂ O exchange, 1 H, CHHOH), 3.41-3.28 (m, 2 H, ArCHCHHOH), 1.51 (s, 9 H, t-Bu); ¹³ C NMR ((CD₃)₂ SO) d 153.2, 151.6 (2×NCO₂), 143 (br, 138.6, 136.7, 126.4 (C-6,8,9 and i C of Ph), 128.3, 127.96, 127.90 (o, m, p C of Ph), 124.4, 112.1, 105.0 (C-4,5,7), 79.7 (OCMe₃), 65.5, 63.9 (OCH₂ Ph, CH₂ OH), 51.4 (C-2), 41.2 (C-3), 28.0 (C(CH₃)₃); MS (DEI) m/z 398 (4%, M⁺); HRMS calcd. for C₂₂ H₂₆ N₂ O₅ 398.18417, found 398.18402.

Methanesulfonyl chloride (0.25 mL, 3.2 mmol) was added to a solution of the mixture obtained from the previous reaction (ca. 1.8 mmol of alcohol) and Et₃ N (0.50 mL, 3.6 mmol) in CH₂ Cl₂ (60 mL) at 0° C., and the mixture was stirred for 15 min. Aqueous NaHCO₃ was added, the mixture was extracted with CH₂ Cl₂ (×2) and the extracts dried (Na₂ SO₄) and evaporated. Flash chromatography on silica gel, eluting with CHCl₃.EtOAc (20:1 then 10:1) gave 6-[(benzyloxycarbonyl)amino]-1-(t-butyloxycarbonyl)-3-[(methanesulfonyloxy)methyl]indoline as a white foam (0.79 g, 93% for two steps). ¹ H NMR (CDCl₃) d 7.73 (s, 1 H, H-7), 7.41-7.3 1 (m, 5 H, Ph), 7.12 (d, J=8.1 Hz, 1 H, H-4), 6.73 (s, 1 H, H-5), 5.19 (s, 2 H, OCH₂ Ph), 4.32 (dd, J=9.9, 5.5 Hz, 1 H, CHHOSO₂ Me), 4.18 (dd, J=9.9, 8.1 Hz, 1 H, CHHOSO₂ Me), 4.11-4.02 (m, 1 H, NCHH), 3.92-3.84 (m, 1 H, NCHH), 3.72-3.62 (m, 1 H, H-3), 2.96 (s, 3 H, OSO₂ Me), 1.56 (s, 9 H, t-Bu); ¹³ C NMR (CDCl₃) d 153.2, 152.1 (2×NCO₂), 143.9, 138.7, 136.0, 123.6 (C-6,8,9 and i C of Ph), 128.6, 128.3 (br) (o, m, p C of Ph), 124.9, 112.7, 105.9 (C-4,5,7), 81.2 (OCMe₃), 71.0 (CH₂ OSO₂), 67.0 (OCH₂ Ph), 51.1 (C-2), 39.1 (C-3), 37.5 (OSO₂ CH₃), 28.4 (C(CH₃)₃); MS (DEI) m/z 476 (5%, M⁺), 91 (100%, C₇ H₇); HRMS calcd. for C₂₃ H₂₈ N₂ O₇ S 476.16172, found 476.16070.

The above benzyloxycarbonylaminoindoline (306 mg, 0.64 mmol) was stirred in HCl-saturated EtOAc (10 mL) at 20° C. for 1 h (until tlc indicated complete reaction) and the mixture was evaporated. 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI, 0.37 g, 1.9 mmol) and 5,6,7-trimethoxyindole-2-carboxylic acid [Y. Fukuda, Y. Itoh, K. Nakatani, and S. Terashima, Tetrahedron, 1994, 50, 2793-2808] (161 mg, 0.64 mmol) in DMF (15 mL) were added to the crude indoline hydrochloride, and the mixture stirred at 20° C. under nitrogen for 22 h. The DMF was evaporated, the residue was dissolved in EtOAc and water, extracted once more with EtOAc, and the organic extracts were dried (Na₂ SO₄) and evaporated. Dry column chromatography of the residue on silica gel, eluting with EtOAc/petroleum ether (1:1), gave 6-[(benzyloxycarbonyl)amino]-3-[(methanesulfonyloxy)methyl]-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]indoline as a pale pink crystalline solid (209 mg, 53%), mp (EtOAc/petroleum ether) 153-154° C. ¹ H NMR ((CD₃)₂ SO) d 11.44 (s, 1 H, indole NH), 9.85 (s, 1 H, carbamate NH), 8.38 (s, 1 H, H-7), 7.46-7.33 (m, 5 H, Ph), 7.33 (d, J=8.2 Hz, 1 H, H-4), 7.25 (dd, J=8.2, 1.8 Hz, 1 H, H-5), 7.03 (d, J=1.9 Hz, 1 H, H-3'), 6.95 (s, 1 H, H-4'), 5.15 (s, 2 H, OCH₂ Ph), 4.62 (apparent t, J=10 Hz, 1 H, CH₂), 4.45 (dd, J=9.8, 5.1 Hz, 1 H, CH₂), 4.35 (dd, J=9.8, 7.2 Hz, 1 H, CH₂), 4.27 (dd, J=10.9, 5.3 Hz, 1 H, CH₂), 3.93 (s, 3 H, OCH₃), 3.87-3.80 (m, 1 H, H-3), 3.81 (s, 3 H, OCH₃), 3.80 (s, 3 H, OCH₃), 3.18 (s, 3 H, OSO₂ Me). ¹³ C NMR d 160.1, 153.3, 149.1, 144.0, 139.8, 139.1, 139.0, 136.6, 130.8, 124 6, 123.1 (C-6,8,9,2',5',6',7',8',9', i C of Ph, NCO, NCO₂, one peak not observed), 128.4, 128.0, 127.9 (o, m, p C of Ph), 125.3, 113.9, 107.7, 106.1, 98.0 (C-4,5,7,3',4'), 71.3 (CH₂ OSO₂), 65.6 (OCH₂ Ph), 61.0, 60.9, 55.9 (3×OCH₃), 53.0 (C-2), 39.3 (C-3), 36.5 (OSO₂ CH₃). Anal. Calculated for C₃₀ H₃₁ N₃ O₉ S.0.5EtOAc: C, 58.8; H, 5.4; N, 6.4. Found: C, 58.7; H, 5.3; N, 6.6%.

A solution of ammonium formate (0.24 g, 3.8 mmol) in water (12 mL) was added to the above 6-[(benzyloxycarbonyl)indoline (233 mg, 0.38 mmol) and Pd/C (5%, 100 mg) in THF (50 mL) and the mixture was stirred at 20° C. More Pd/C (30 mg) was added after 70 min, and after 100 min (tlc indicates complete reaction) the catalyst was filtered off and washed with EtOAc. The filtrate was diluted with aq. NaCl, extracted with EtOAc (×2), and the extracts dried (Na₂ SO₄) and evaporated. Dry column chromatography (eluting with 2:1 EtOAc:petroleum ether) gave 6-amino-3-[(methanesulfonyloxy)-methyl]-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]indoline (25) as a pale yellow foam (154 mg, 85%). This mesylate (150 mg, 0.32 mmol) and LiCl (0.13 g, 3.2 mmol) were stirred in DMF (5 mL) at 70° C. under nitrogen for 80 min, and the DMF evaporated. The residue was dissolved in EtOAc and water, extracted once more with EtOAc, and the organic extracts dried (Na₂ SO₄) and evaporated. Dry column chromatography, eluting with EtOAc/petroleum ether (1:1) gave 6-amino-3-(chloromethyl)-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]indoline (32) (87 mg, 66%), mp (EtOAc/Et₂ O) 173-174° C. ¹ H NMR [(CD₃)₂ SO] δ 11.36 (d, J=1.6 Hz, 1 H, NH), 7.44 (br s, 1 H, H-7), 7.05 (d, J=8.0 Hz, 1 H, H-4), 6.96 (d, J=2.1 Hz, 1 H, H-3'), 6.95 (s, 1 H, H-4'), 6.30 (dd, J=8.0, 2.2 Hz, 1 H, H-5), 5.18 (s, 2 H, NH₂), 4.54 (dd, J=10.8, 8.7 Hz, 1 H, NCHH), 4.20 (dd, J=10.8, 4.4 Hz, 1 H, NCHH), 3.93 (s, 3 H, OCH₃), 3.91 (dd, J=9.9, 3.5 Hz, 1 H, CHHCl), 3.81 (s, 3 H, OCH₃), 3.79 (s, 3 H, OCH₃), 3.74-3.60 (m, 2 H, CHCHHCl). ¹³ C NMR δ 159.9, 149.0, 144.2, 139.6, 139.0, 131.2, 125.1, 123.1, 118.8 (C-6,8,9,2',5',6',7',8',9', NCO, one peak not observed), 124.7, 109.5, 105.6, 102.9, 98.0 (C-4,5,7,3',4'), 61.0, 60.9, 55.9 (3×OCH₃), 54.5 (C-2), 47.9 (CH₂ Cl), 41.8 (C-3). Anal. Calculated for C₁₂ H₂₂ ClN₃ O₄): C, 60.7; H, 5.3; N, 10.1. Found: C, 60.7; H, 5.4; N, 9.8%.

INDUSTRIAL APPLICATION

As will be apparent from the above description and examples, this invention provides improved methods for cancer therapy. The advantages of the invention are largely achieved through the selection and use of RACP.

RACP retain the selectivity of BD for hypoxic microenvironments but provide the following additional advantages:

(a) Reduction is confined to the radiation field, greatly diminishing systemic toxicity. This feature takes advantage of recent technological advances in computerised radiation treatment planning and delivery systems which now offer high-precision matching of the radiation field contours to the tumour in three dimensions (conformal treatment).

(b) The forward reduction is inhibited in oxic cells. The very rapid reaction of the major reducing species generated by radiolysis of water, e_(aq) ⁻ and H., with O₂ would ensure that the rate of forward reduction is greatly diminished in the presence of O₂. In contrast, the rate of the forward reduction by bioreductive enzymes is probably insensitive to O₂ in most cases, the inhibition of net reduction being due only to back-oxidation by O₂. For the RAC mechanismn, O₂ can inhibit the forward reduction, as well as reoxidising the one-electron product, and is therefore expected to provide greater inhibition by O₂ (hypoxic selectivity) than achieved with BD.

(c) There is no competing two-electron (O₂ -insensitive) reduction by radiolytic reduction since this is an obligate one-electron process, further enhancing selectivity relative to enzymatic activation.

(d) Activation would be independent of the peculiarities of reductive enzyme expression of the tumour.

(e) It would be possible to use high dose rate irradiation to lower O₂ concentrations further. The (enzymatic) activation of some BD is so readily inhibited by traces of O₂ that many radiobiologically hypoxic cells may not be sensitive. RAC are expected to be at least as sensitive to trace O₂ ((b) above), but delivery of the radiation at a high dose rate (ca 5 Gy.s⁻¹) would scavenge sufficient O₂ to make radiobiologically hypoxic tissue (<1 μM O₂) completely anoxic during the irradiation period.

Those persons skilled in the art will understand that the specific description provided above is exemplary only and that the present invention is not limited thereto. 

What is claimed is:
 1. A method of treating neoplastic disease which comprises the steps of:(a) administering to a patient in need of such treatment an effective amount of a radiation-activated cytotoxin prodrug (RACP) which has low toxicity, which is reducible by reducing agents generated by the radiolysis of water and which, upon reduction, releases a sufficient amount of a cytotoxic effector of sufficient cytotoxic potency to kill tumor cells, wherein the RACP is a compound of formula I ##STR32## wherein R¹ represents H or C₁ -C₄ alkyl unsubstituted or substituted with hydroxyl, ether, amino, methylamino or dimethylamino groups; n is 0, 1 or 2, and each M is independently selected from NO₂, CF₃, CH₂ OR¹, COR¹, CONHR¹, OR¹, NR¹ R¹ and SO₂ R¹ wherein R¹ is as defined above; wherein arom is a single benzene ring or a 5- or 6-membered aromatic heterocycle containing one or two heteroatoms independently selected from O, S and N; L- is a pharmacologically acceptable counterion; K is H or Me; and wherein R² is represented by:(i) a radical of formula II ##STR33## where X is halogen or OSO₂ R¹ (where R¹ is as defined above);A and B are each H or collectively represent an unsubstituted or substituted fused benzene or pyrrole ring; W is selected from SO₂ R¹ (where R¹ is as defined above) and the structures IIa and IIb, where:D is CH or N; E is NH or O; each Q is independently selected from OR¹ and NR¹ R¹ wherein R¹ is as defined above; n is 0, 1, 2 or 3; and HET represents a 5- or 6-membered carbocycle or heterocycle containing one or two heteroatoms independently selected from O, S, and N; (ii) a radical of formula III ##STR34## where X, A, B, Q and n are as defined above; and each D is independently CH or N; andeach E is independently NH or O; (iii) a radical of formula IV ##STR35## where Z is H or NHR¹ (where R¹ is as defined above); n is 0, 1 2, or 3; andeach Y is independently selected from Me and OMe; or (iv) a radical of formula V ##STR36## where each J is independently H or OH; and T is NMe₂, or a moiety of the formula ##STR37## wherein n, M, arom, K and R¹ are as defined for formula I above; and (b) irradiating said tumor cells with ionizing radiation to reduce the prodrug which is present at the locus of said tumor cells to release said cytotoxic effector.
 2. A method as claimed in claim 1 wherein the RACP is a compound of formula I wherein R² is a radical of formula II.
 3. A method as claimed in claim 1 wherein the RACP is a compound of formula I wherein R² is a radical of formula III.
 4. A method as claimed in claim 1 wherein the RACP is a compound of formula I wherein R² is a radical of formula IV.
 5. A method as claimed in claim 1 wherein the RACP is a compound of formula I wherein R² is a radical of formula V.
 6. A method as claimed in claim 1 wherein the RACP is a compound of formula Ia ##STR38## wherein R² and L- are defined as in claim 2 and M is one of H, CF₃, CH₂ OR¹, COR¹, CONHR¹, OR¹, NR¹ R¹ and SO₂ R¹ where R¹ represents H or C₁ -C₄ alkyl unsubstituted or substituted with hydroxyl, ether, amino, methylamino or dimethylamino groups.
 7. A method of treating neoplastic disease which comprises the steps of:(a) administering to a patient in need of such treatment an effective amount of a radiation-activated cytotoxin prodrug (RACP) which has low toxicity, which is reducible by reducing agents generated by the radiolysis of water and which, upon reduction, releases a sufficient amount of a cytotoxic effector of sufficient cytotoxic potency to kill tumor cells wherein the RACP is a compound of formula (VI) ##STR39## wherein each R¹ is independently H or C₁ -C₄ alkyl unsubstituted or substituted with hydroxyl, ether, amino, methylamino or dimethylamino groups; U and V are both CH₂ CH₂ Cl, or U is H and V is a radical of formula II ##STR40## wherein X is halogen or OSO₂ R¹ (where R¹ is as defined above); A and B are each H or collectively represent an optionally substituted fused benzene or pyrrole ring; W is selected from SO₂ R¹ (wherein R¹ is as defined above) and the structures IIa and IIb, where: D is CH or N; E is NH or O; each Q is independently selected from OR¹ and NR¹ R¹ wherein R¹ is as defined above; n is 0, 1, 2 or 3; and HET represents a 5- or 6-membered carbocycle or heterocycle containing one or two heteroatoms independently selected from O, S and N; or a radical of formula III ##STR41## where X, A, B, Q and n are as defined above; and each D is independently CH or N; and each E is independently NH or O; and L- is a pharmaceutically acceptable anion; and (b) irradiating said tumor cells with ionizing radiation to reduce the prodrug which is present at the locus of said tumor cells to release said cytotoxic effector.
 8. A method as claimed in claim 7 wherein the RACP is bis(3-methyl-2,4-pentanedionato)(N,N-bis(2-chloroethyl)ethylenediamine)cobalt (III) chloride.
 9. A method of treating neoplastic disease which comprises the steps of(a) administering to a patient in need of such treatment an effective amount of a radiation-activated cytotoxin prodrug (RACP) which has low toxicity, which is reducible by reducing agents generated by the radiolysis of water and which, upon reduction, releases a sufficient amount of a cytotoxic effector of sufficient cytotoxic potency to kill tumor cells, wherein the RACP is a compound of formula VII: ##STR42## wherein n is 0, 1 or 2, and each M is independently selected from the group consisting of NO₂, CF₃, CH₂ OR¹, COR¹, CONHR¹, OR¹, NR¹ R¹ and SO₂ R¹ wherein R¹ represents H or C₁ -C₄ alkyl optionally substituted with hydroxyl, ether, amino, methylamino, or dimethylamino groups; andarom is a single benzene ring or a five- or six-membered aromatic heterocycle containing one or two heteroatoms independently selected from the group consisting of O, S and N; and L- is a pharmacologically acceptable counterion; (b) irradiating said tumor cells with ionizing radiation to reduce the prodrug which is present at the locus of said tumor cells to release said cytotoxic effector.
 10. A method as claimed in claim 9 wherein the RACP is selected from the following compounds:N,N-bis(2-chloroethyl)-N-methyl-N-[(1-methyl-4-nitro-5-imidazolyl)-methyl]ammonium chloride, N,N-bis(2-chloroethyl-N-methyl-N-(2-nitrobenzyl)ammonium chloride, N,N-bis(2-chloroethyl-N-methyl-N-(3-nitrobenzyl)ammonium chloride, N,N-bis(2-chloroethyl-N-methyl-N-(4-nitrobenzyl)ammonium chloride, N,N-bis(2-chloroethyl-N-methyl-N-(4-methylsulfonyl)benzyl)ammonium chloride, and N,N-bis(2-chloroethyl-N-methyl-N-benzylammonium chloride.
 11. A method of treating neoplastic disease which comprises the steps of:(a) administering to a patient in need of such treatment an effective amount of a radiation-activated cytotoxin prodrug (RACP) which has low toxicity, which is reducible by reducing agents generated by the radiolysis of water and which, upon reduction, releases a sufficient amount of a cytotoxic effector of sufficient cytotoxic potency to kill tumor cells wherein the RACP is a compound of formula (VIII) ##STR43## wherein Y and Z are as defined for formula IV, T is Co(III) or Cr(III), n is from 2 to 6, m is 2 or 3, and R³, R⁴, R⁵ and R⁶ are each independently selected from CN, halogen, SCN, H₂ O and NHR¹ wherein R¹ is as defined in claim 2, or together represent 3-R⁷ acetonylacetonato where R⁷ is H, Me, NO₂, CN, SCN or SPh where Ph is a benzene ring unsubstituted or substituted with up to two groups independently selected from Me, OMe, NO₂ and NMe₂); and (b) irradiating said tumor cells with ionizing radiation to reduce the prodrug which is present at the locus of said tumor cells to release said cytotoxic effector.
 12. A compound of formula I: ##STR44## wherein R¹ represents H or C₁ -C₄ alkyl optionally substituted with hydroxyl, ether, amino, methylamino or dimethylamino groups;n is 0, 1 or 2, and each M is independently selected from NO₂, CF₃, CH₂ OR¹, COR¹, CONHR¹, OR¹, NR¹ R¹ and SO₂ R¹ wherein R¹ is as defined above; wherein arom is a single benzene ring or a 5- or 6-membered aromatic heterocycle containing one or two heteroatoms independently selected from O, S and N; L⁻ is a pharmacologically acceptable counterion; K is H or Me; and wherein R² is represented by:(i) a radical of formula II ##STR45## where X is halogen or OSO₂ R¹ (where R¹ is as defined above);A and B are each H or collectively represent an unsubstituted or substituted fused benzene or pyrrole ring; W is selected from SO₂ R¹ (where R¹ is as defined above) and the structures IIa and IIb, where:D is CH or N; E is NH or O; each Q is independently selected from OR¹ and NR¹ R¹ wherein R¹ is as defined above; n is 0, 1, 2 or 3; and HET represents a 5- or 6-membered carbocycle or heterocycle containing one or two heteroatoms independently selected from O, S and N; (ii) a radical of formula III ##STR46## where X, A, B, Q and n are as defined above; and each D is independently CH or N; andeach E is independently NH or O; (iii) a radical of formula IV ##STR47## where Z is H or NHR¹ (where R¹ is as defined above); n is 0, 1, 2 or 3; andeach Y is independently selected from Me and OMe; or (iv) a radical of formula V ##STR48## where each J is independently H or OH; and T is NMe₂ or a moiety of formula ##STR49## wherein n, M, arom, K and R¹ are as defined for formula I above.
 13. A compound of formula I as claimed in claim 12 wherein R² is a radical of formula II.
 14. A compound as claimed in claim 13 wherein the compound is selected from the following:3-(chloromethyl)-6-[N,N-dimethyl-N-(4-nitrobenzyl)-ammonio]-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]indoline chloride, and 3-(chloromethyl)-6-[N,N-dimethyl-N-(2-nitrobenzyl)-ammonio]-1-[(5',6',7'-trimethoxyindol-2'-yl)carbonyl]indoline chloride.
 15. A compound of formula I as claimed in claim 12 wherein R² is a radical of formula III.
 16. A compound of formula I as claimed in claim 12 wherein R² is a radical of formula IV.
 17. A compound as claimed in claim 16 wherein the compound is selected from the following:2-[N-(acridin-4-yl)carbonyl]aminoethyl-(dimethyl)-4-nitrobenzylammonium brormide, 2-[N-(acridin-4-yl)carbonyl]aminoethyl-(dimethyl)-(5-nitro-2-thienyl)methylammonium chloride, 2-[N-(9-amino-5-methylacridin-4-yl)carbonyl]aminoethyl-(dimethyl)-4-nitrobenzylammonium bromide, 2-[N-(9-amino-5-methylacridin-4-yl)carbonyl]aminoethyl-(dimethyl)-2-nitrobenzyl]ammonium chloride, 2-[N-(9-amino-5-methylacridin-4-yl)carbonyl]aminoethyl-(dimethyl)-5-nitro-2-thienylmethylammonium chloride, 2-[N-(9-amino-5-methylacridin-4-yl)carbonyl]aminoethyl-(dimethyl)-2-[4-morpholino-5-nitro-4-thiazolylmethyl]ammonium chloride, 2-(N-[9-amino-5-methylacridin-5-yl]carbonyl)aminoethyl-(dimethyl)[1-methyl-5-nitro-2-pyrrolyl]methylammonium chloride, 2-(N-[9-amino-5-methylacridin-4-yl]carbonyl)aminoethyl-(dimethyl)-(1-methyl-4-nitro-5-imidazolyl)methylammonium chloride, and 2-(N-[9-amino-5-methylacridin-4-yl]carbonyl)aminoethyl-(dimethyl)-(3-nitro-2-thienyl)methylammonium chloride.
 18. A compound of formula I as claimed in claim 12 wherein R² is a radical of formula V.
 19. A compound as claimed in claim 18 wherein the compound is selected from the following:
 1. 4-bis[((2-(4-nitrobenzyl)dimethylammonium)-ethyl)amino]-9,10-anthracenedione dichloride,1-(2-(4-nitrobenzyl)dimethylaminoethylammonium)-4-(2-dimethylamino)ethylammino-9,10-anthracenedione acetate, 1,4-bis[(2-(4-nitrobenzyl)dimethyl-ammonium)ethylamino]-5,8-dihydroxy-9,10-anthracenedione dichloride, and 1-[(2-(4-nitrobenzyl)dimethylammonium)ethylamino]-4-[(2-dimethylamino)ethylamino]-5,8-dihydroxy-9,10-anthracenedione chloride.
 20. A compound as claimed in claim 12 of formula Ia: ##STR50## wherein R² and L⁻ are defined as in formula I, and M is one of H, CF₃, CH₂ OR¹, COR¹, CONHR¹, OR¹, NR¹ R¹ or SO₂ R¹ where R¹ represents H or C₁ -C₄ alkyl unsubstituted or substituted with hydroxyl, ether, amino, methylamino or dimethylamino groups.
 21. A compound of formula VIII: ##STR51## wherein Y and Z are as defined for formula IV, T is Co(III) or Cr(III), n is from 2 to 6, m is 2 or 3, and R³, R⁴, R⁵ and R⁶ are each independently selected from CN, halogen, SCN, H₂ O and NHR¹ wherein R¹ is as defined in claim 1, or together represent 3-R⁷ acetonylacetonato (where R⁷ is H, Me, NO₂, CN, SCN or SPh).
 22. A compound as claimed in claim 21 which is bis(3-methyl-2,4-pentanedionato)-(N-[3-[(2-aminoethyl)-amino]propyl]acridine-4-carboxamide)cobalt(III) perchlorate.
 23. A pharmaceutical composition for use in treating neoplastic disease, comprising a RACP compound of the formula I or VIII, as defined in claim 1, and a pharmaceutically acceptable carrier or vehicle therefor.
 24. A pharmaceutical composition as claimed in claim 23, wherein the RACP compound is a compound as defined above.
 25. A pharmaceutical composition as claimed in claim 23, which is in an injectable form. 